LoneLou, I wouldnt like to do the, oh hes a cheat get rid of him thing, but I would just like to share a few things.
My mum was married to my dad, they had me, I was 2 he left, then came back, mum got pregnant, he left. Then came back, in the mean time he got his girlfriend pregnant, so he left, then, guess what came back!! this time got mum pregnant, so now wife and mistress pregnant at the same time, so finally mum threw him out.
Sometimes certain men, think only of themselves and run away from responsibility, and he sounds like he is regretful of the pregnant girlfriend, but thats not your problem, and itss not your place to save him, he now has serious baggage to bring into this relationship, and it will affect you, I poersonally would leave him well alone, if your heart is screaming for him, i understand but sometimes we have to override our emotions and think with a clear head. My mum, loves my little brothers and is grateful for them, but the trouble that man caused by thinking of himself still rings through to this day 30 years later.
Please dont just consider your child, you have to consider yourself, you deserve a great relationship, and trust is part of that, and if you lack trust, the heartache will continue, whether he is faithful or not.