I’m so sorry you are going through this. Tbh I’m not sure what the therapist is thinking! I’m all for keeping couples together, but the way he has treated you is unforgivable and he clearly feels no remorse (telling you what the other woman did for him...wtf? Are you supposed to compete or “live up”?)
People can change, sure, but they need to hold themselves accountable. Clearly he doesn’t.
So what’s to stop him doing the same thing five years from now. Ten. Twenty. If he manages to convince you it was somehow your fault, due to arguing, then the sky’s the limit. Because I can promise you that no marriage is without its stresses, whether that’s arguments, boredom, grief, poverty, fading libidos, addiction, illness, you name it. If he can cheat on you with multiple women so early on in your life together (and while you are pregnant, no less), just imagine what he can do to fuck up the rest of your life?
Not my usual refrain either, but LTB. You deserve so much more.