Relationship advice I need ASAP

Hi everyone,

I really need help and some advice I’m nearly 20 years old my boyfriend and I have been together since we were 14 and at the beginning of our relationship I had a really close friend who was a boy and relationship would never work between us but he hated my boyfriend ans they ended in a fight and I had to choose so I chose my boyfriend and for some reason I keep thinking about my old best friend miss our times together and I keep thinking about my ex who used me and made me heartbroken I do love my boyfriend but I feel awful about thinking about other men is this normal it gets to my stomach when I think about a lift without him someone help me and advice me on if this is normal or if I’m being a dick thank you