Oh hon :( It' must be really hard and everyone knows what it's like to be in love, love is blind and all that.
He married and made a long term commitment to another woman and is now having a baby with her, so I guess that side of the relationship was Ok at least before the pregnancy.
I know things can change but his world is about to be changed dramatically with the arrival of his child, a life long commitment, and helping look after the child and it's mother who he wll now be forever tied to.
Even if he did leave, I don't imagine the fall out would be at all easy, leaving a pregnant wife or new born child, the effect on family and friends would not, I don't imagine, be pretty and I don't know how you would be able to cope with the backlash as well and potential reaction of his family and friends and no short term thing with a new child on the way.
It doesn't bode well for a happy new relationship.
I'm not saying it might not work out, now or in the future, but, in the meantime, hold your head up high and walk away and find someone who can give their all to you, you deserve better hon xxx