I loved a girl who had several boyfriends all said she was a bad girl but still I loved her I made frendship with her but I had no courage to propose her now she is far away and is in deeply love with another guy a friend of mine and is a good girl now how do I forget it please help my studies are degraded because of this

Every problem that you have from this, is rooted back to you. You are the reason your studies are degrading and you are the reason you can't stop thinking about her.

Stop thinking about her and quit living in the past focus on the future.

You tell yourself "that's life" and you get over it. You are the one who did not speak up. Learn from that lesson.

Find a new girl and don't hesitate