You and Snape became friends during the train ride to Hogwarts. You went into Snape's compartment because the other compartments were filled and you had no space to sit there. You peeped into a raven haired boy's compartment and you asked "Hi, do you mind if I sit here?" and he replied "Yeah, whatever don't bother me all right?" and you shuffled in nervously as you wondered which side of bed he got up from and why he was so cranky. "So, uhh... do you mind if I ask you your name?'' you asked him hesitantly, nervous of making him cranky but he just looked at you and replied "It's Severus. Unless of course you call me some other names, like Slimeball or whatever'' and you were confused

"Why would I want to call you that?'' you asked him curiously and he replied with a sour expression "There were other people who called me that. Two guys on the same train and unfortunately coming to Hogwarts as first years'' and you felt a bit mad. The school year didn't even start, you didn't know anyone other than him but you already felt mad about people calling him names. What did he do to be on the receiving end of of their name calling wasn't your primary thought for now. "Well that's not nice, if I see them I'll hex them'' you said and he replied "Thanks but I can take care of myself you know" and you meekly answered "Oh'' but Snape felt a bit bad for once for speaking to you like that. He knew you were only trying to help and truth be told, he'd never been received help before by anyone. It was a strange feeling and the very fact that you wanted to hex the people who'd called him names he felt touched by your kindness

Just then the lady with the lunch trolley came and she asked you if you guys wanted anything. You purchased some sweets from her and you shared them with Snape and he was a bit surprised that you decided to share your sweets with him. At first he refused to take them since they were yours after all and you'd spent your money but when you insisted and told him you'd be sad if he didn't take one, that's when he gave in and sighed and took one to please you. Somehow for some reason he didn't want to see you upset. Call him crazy, but in the short time he's met you and interacted with you, he's already gotten a strange feeling for you, a feeling of possessiveness over you. He had an aim to get into the Slytherin house and he hoped that you'd end up in Slytherin too

While you both were talking two guys peeped through your compartment door who were none other than James and Sirius. "Oh lookie what we have here, looks like Slimeball has found himself a lover~'' snickered Sirius and you narrowed your eyes at them but Snape had a sour look on his face and didn't reply anything. Truth be told he WISHED that was the case, you were bright, intelligent and extremely good looking. He'd hoped that you'd be his pretty soon but he had a feeling these two idiots would ruin things with you. However you got up from your seat and spoke "He's done nothing to you both so leave him alone'' and James replied "Yes he has, he exists. And sweetheart, it's best not to get involved, goodness knows who might do what to you'' and smirked at you, hoping you'd swoon or something but you just stood there unimpressed

That's what Snape felt a bit mad, took out his wand and hexed them out of the compartment. You turned to him and spoke "You shouldn't have done that you know, what if they're injured or something? We might get into trouble'' you said feeling worried. You didn't want to get kicked out of Hogwarts, not when the school year hasn't even started yet. "Nothing's going to happen to those prats don't worry. We won't be in trouble and I advise you to not concern yourself with them, they'd dared to insult you after all'' and you couldn't help but feel touched he's stood up for you. Snape was furious to say the least when James looked at you like that, he was such a git. He couldn't let him steal you away from him so Snape made sure to stick close by you at all times. When you guys and the rest of the other First Years were crossing the Great Lake in the boats, you couldn't help but marvel at the sight of the starry night sky with the castle of Hogwarts decorated with bright lights and lanterns which you could see from far and you stared in awe as you gushed to Snape about how wonderful the place was

Snape couldn't help but feel happy when you were sitting next to him. In a short amount of time he's already grown obsessed with you and when he saw the excited glint in your eyes and your smile, he wanted to do everything he could to make sure your beautiful smile stayed that way. He'd hurt anyone who dared to take it from you. Soon it was time for your Sorting and you felt nervous. "Sev, what if we don't end up in the same house? I hope we'll still be friends'' you muttered and he grabbed your hand in his and replied "Don't worry, we'll still be friends'' and of course, as hoped he got sorted into Slytherin but you got sorted into Gryffindor with James and Sirius as well. Snape heard stories about how Slytherin and Gryffindor were rivals or whatever but he found them to be quite stupid. But when you were sorted into another house especially with the guys he'd hated the most, he felt panicked. He couldn't lose you, so he made sure to spend time with you

You'd always stick up for him and even though people from your own house had prejudiced notions about Slytherins, you replied that not all Slytherins were bad and you asked them to STFU. Snape loved spending time with you, you were a bit weak in Potions so he offered to teach you. You both would also practice spells with each other, but he wouldn't use any harmful ones on you, the last thing he wants to do is hurt the one he loves. However one day when you were in the 5th year, someone decided to ask you out and you said you needed some time to think about it. You decided to go to Snape to ask for his advice and thoughts on the situation. After breakfast was done for you both, you'd always hang out at the library since there would still be a lot of time left for classes to start

"Sev, someone from Ravenclaw confessed to me and I don't know what to do, any advice? I mean, I think he's a pretty good friend but... I'm a bit confused'' you said and Snape stopped his writing and he felt so mad, his quill blotted the entire parchment but he didn't care. How DARE someone try to steal you away from him? His hand was twitching in anger and he wanted to torture that little git whoever dared to ask you out. However Snape was also smart, he knew if he hexed that rascal in front of you for no good reason you'd no longer be friends with him or be with him and that's something he didn't want happening. He regretted not asking you out sooner and waiting this long, he was nervous that if you reject his confession things would be awkward between the two of you but now there was no avoiding it. Snape had to have you for himself, you were destined to be his and ONLY his, not anyone else's

Snape told you some rumor about the guy who asked you out, you avoided him and rejected his confession which made Snape delightful. When he caught the guy alone by himself, he dragged him to a secluded spot, cast a silencing charm on him and used the Cruciatus curse on him. His screams of pain were deaf on all ears at Hogwarts because of the Silencing charm he's cast on him. Then Snape hissed "Be thankful I'm sparing your pathetic life and not killing you. I'll get expelled from here if I do waste my time and taint my hands killing you and then I'll be away from MY Y/N, so if you know what's good for you, stay the hell away from them. If you dare open your mouth to someone about this, you're going to regret it'' and the other dude nodded in agreement

After that incident, Snape couldn't take any more chances of people stealing you away from him which was why he asked you out immediately and surprisingly, you said yes. For your sake he stopped dissing the Gryffindors too much but when he sees Sirius and James he can't help but get mad and he does his best to make you stay the hell away from them. He doesn't leave till he sees you go into your dorm and follows you all around the place like a guard dog. Now, he had you right where he wanted and he had no intention of letting you go.