Help !!!

What do you do when you've begun becoming attracted to someone you shouldn't while you have a boyfriend???? I've been with my man for over a year and a half and I got a new job and one of my coworkers and I have a past and now I'm suddenly interested in him again and we snapchat all day long and stuff.

I never see my boyfriend and we both work so we barely talk but I have everything I've ever wanted planned out with my bf but idk what to do about being heavily attracted to this other guy