Is it normal for you to feel like your bf will dump you for one of your friends?

My bf is really sweet but when ever i get a crush or bf i am jelouse of my friends because i think he will dump me for them. I only say this because I believe my friends are prettier then me and i am really shy so it is hard for me to get a bf and when i do get one i feel like he will dump me at any moment enen tho that is not tru plz help i am in grade 7 and I am new at dating so plz help me