Do you know this feeling?

I’m in this situation currently. I’m in a serious relationship but I’m scared feelings for a boy I used to like might resurface. I know my feelings for my boyfriend are sincere, I just worry about not being able to control those old feelings and having to tell him, breaking his heart and ruining my current relationship.
Do you know this?
Did the resurfacing of feelings for an ex ever happen to you?
And most importantly: did you tell the partner you were/ are with about your fears?
Basically, I’m trying to figure out whether I should tell my boyfriend or not. I don’t want to scare him, I want to stay with him. But I feel so bad worrying about this and not telling him.