I'm in love with my friends boyfriend :/

So I've known this boy for about two years now, I've spent a lot of time around him in school and we get along so well, better than I do with most people. The only problem is, he has a girlfriend of about a year now. I've only recently noticed my feelings towards him changing and I dont know what to do about it. I've heard rumours that he used to like me way back when we first met and now I have a whirlwind of emotions going on in my head. I'm finding it difficult to see them around eachother. I never used to notice myself getting jealous of their relationship but now I can't be around them without wishing I was in her shoes. She is a good friend of mine and I'm stuck on how I should go about it, because I can't go on like this. Any advice?😞