Why is she like this?

Hey guys wats up? Well I have this problem. Ok so I had this best teaacher last year and she was really nice to me and this yer she doesn't even say hi or anything like this, I'm not gay or bi anything lke that I'm straight why is she lie this . And if she doesn't talk to me I won't talk to her it's just like you kno me begging and because im scare she might not say hi back or sy hi but in a mean way wat should I do? Thanks