Short Answer? You're not married, so it's over. Now. Ask the people in your life who have shown the utmost love and respect for you and they would likely agree. It's painful and will be for a while, but whether he gets his act together or you find another committed man of God, a lifetime with each other AND/OR raising children together DEMANDS better and will be worth it.
Get in your bible. Get with your friends and family. Get in your church. But you need now more than ever, the conviction to be strong and demand a better man as a husband.
I read the book, "I Kissed Dating Goodbye" and found there to be much wisdom in the idea of courting over dating. Its also a much better protection from the temptation of sexual sin while emotional and spiritual intimacy is developing but obviously a much tougher commitment for someone who was so immersed in modern secular culture where sexual promiscuity was a fact of life.
Sin is like a drug in the sense that you are always somewhat predisposed. Even if he HAD repented and stayed faithful, there are emotional and physical issues that remain for you and him....you slightly acknowledge that in your language. Sexual Forgiveness does not remove consequence.
The fact that he even allows himself to be in a situation where temptation could strike is evidence that he is an immature, foolish young man at best...possibly narcissistic, self absorbed and possibly false faith...who is nowhere near being a husband or father. (A foolish man resists temptation, a wise man runs from it! He doesnt even put himself in its path...he avoids even the appearance of impropriety.)
The fact that you didn't see these flags and demand more means you're not quite ready. Keep working on being a strong woman of God and give yourself and your future children the love, peace and stability of having a godly father.
