Advice loving two people at same time?

I was with my ex 6 years had a baby and was my first love we split up nearly 2 years ago but all of a sudden my love and feeling have come back for him 😭 but I'm in a relationship with another guy and got a 7 month old baby anyone got any advice oh how too sort it out has anyone else been in this situation? I'm torn between too guys but scared too leave the guy I'm with because he threatens too do my ex over and make sure he's dead what would you guys do?