I do feel for you.
You have just had a life changing transformation in your life and your are probably not back to your full self yet, so don't rush into any decision.
I think you do realise that there are two issues here, but you should give yourself a chance to lose the baby brain muddle and at least give yourelf sometime to recover from the pregnancy.
It is difficult, but try to forget about this until you are thinking more clearly as you are confusing the two issues and you need to make sure that you don't so something for the wrong reasons.
In 6 months time at least, you need to decide whether you do love your husband and this is just the thoughts that a lot of mothers have after having a baby, of being unsure of the future or whether there are some other issues.
Questions you should ask yourself then are:
Do I still love my husband or have we drifted to the point of no return?
Does he still love me, does he feel the same way about you?
talk the feelings through
Relationships change over time and a baby changes things and things will never be quite the same in a couple again, this can be one of the hardest times in a relationship.
Sometimes, unfortunately things do not work out and many many couples drift apart and split up after a baby.
You need to work out whether your relationship has evolved as you are now parents and you can go on together. The relationship will be different, but in a good way or whether it is over.
But it should be a discussion between you both.
Only once you have the solution to that issue can you move on to deal with the other issue.
Only if you realise that your relationship is over with your hubbie, should you even consider if you want to pursue "amazing guy",
or if you just want to be remain friends with him, if you both agree that it can go no further than just friends or that you never contact him again.
Whether the guy thought there really was a chance because you kept in touch, I don't know. Ask yourself, were you still flirtatious with him, have you suggested to him of problems in your relationship?
The When Harry Met Sally thing about men and women can't be friends without the sex thing getting in the way is often true.
He chose the wrong time to tell you, but giving him the benefit of the doubt, he is now doing the right thing by not contacting you.
I wish you good luck in this.