first vs second love

hey everyone, i hope you're having a good day.
i'm going to try to keep this short.
my relationship with my first love was toxic and my relationship with my second love is extremely healthy.
i love my boyfriend, i really do but there are times when i think about my ex and what we could be.
i feel so bad for my boyfriend because i know he loves me with all his heart.
i don't know what to do, i really need some advice so please share your thoughts. i'm still young so all this "love" bs is new to me and extremely confusing, lol.