You're not over reacting. My fiance did that when we first found out I am pregnant and a few weeks ago he went to the club and kissed some other female and called me crying bout it. When he got home we talked bout it and I ended up punching him in the jaw, and I can pack a punch lol, but ever since then he hasn't done much or when he does go out he is with his cousin or his best friend, and she will beat his *** if he does something out of pocket. Men do what they know they can get away with. Explain to him how you feel and make it clear that you do not appreciate it and that there will be consequences. Usually they just need to be reassured that baby isn't taking all you love and care from them.
I don't understand how some men can be so sweet and others act single in the streets but if we do the things they do we are the worst ppl in the world.