Me and my SO have a 4 year old son together but there has not been a whole lot of ual activity going on bec?

because I have serious issues with the subject.I think it's dirty and I feel in my heart that people shouldn't have until they're married but a child was produced before this but I don't have any feelings like that towards him.He's threatening to leave me for somebody else but I wish he would wait a little longer and anyway it's just talk,if he wanted somebody else he would've moved on already,Should I let him go or talk to him about how I feel about this or him?