<human>: I [19F] recently started dating my SO [20M]. We met at our local university and despite the minimal length of time that we have been dating, he is definitely the best guy I have been with. I feel myself falling in love with him already. However, I have one concern. He has a long term best friend [20F]. They have been very close since high school, but she moved a few hours away for college. She is visiting home for the break and I got to meet her at a party last night. I'm fairly new to my SO's friend group, so I am uncertain of their dynamics. But I don't receive a good "vibe" from the long term girl best friend. She's attractive and overall a person I would enjoy being friends with, however, I feel like she is almost territorial of my SO. I tried killing her with kindness with no avail. She basically brushed off everything I said and would correct me when I made a mistake in conversation. 
I understand that she was here before me and she certainly knows and understands him better than I do at this point, but I have kind of a bad gut feeling about their relationship. I asked my SO if they had any sort of romantic relationship and he said that he at one time had a crush on her, but there were no reciprocated feelings. I don't know if he ever disclosed his feelings to her. 

Admittedly, I am a high maintenance partner. I need tons of assurance or I question everything. But, I don't want to ruin what could be the beginning of an awesome relationship. Any advice on how to deal with jealousy and insecurity in a healthy way?

Can you condense the text into three sentences or less?
<bot>: How do I [20F] stop being jealous of my SO's [20M] long term best friend [20F]?