Help: Still in love

Hey everyone, I need advise. I met a boy I feel in love with in high school. We spent a lot of time together as friends, nothing ever became romantic (except for my feelings). I haven't spoken to him in 4 years. I went to college, fell in like with other guys, but I have never felt the same way as I felt for him. I am still very close with his sister and family, so I didn't really get closure.. I don't know if that's why I'm still holding on to him? He is in the military and has married a girl that nobody likes. She is very selfish, puts no effort into having a relationship with his family and has cheated on him in the past. It's just hard to know that he is not being treated like he deserves. I hate that I have been daydreaming lately about him breaking up with her. I really don't want that, i just want him to be happy. How do I fully get over him?

Thanks,

Sarah