What do you think

So my boyfriend and I have been together for 6 years,.we have one son and one on the way. He was constantly bringing up a 3 some and I was not comfortable with that, it was becoming overwhelming. So I had enough and told him he could have a pass for one night. I regret it because hes constantly talking to other girls, flirting, making plans ect. He hasn't done anything yet but today I told him I didn't think it was a good idea because the whole thing is stupid and if he really loved me he wouldn't even be thinking of other woman. I also told him that I don't want any problems with other woman or him bringing any STDs home to me. I know hes gunna be upset but if hes that upset and wants somone else I feel like I should just leave him. What do you guys think