@Blueberrymuffin40 - "Good for her" - seriously?! You think it's good that she lied to OP in order to get pregnant? Come on!
I hope you were being sarcastic and it just went over my head 
OP - believe me, it will be much better for you, her and the baby if you end things with her now. Babies do NOT bring people closer together, especially in a relationship where one of the parties was already halfway out the door.
You are effectively leading her up the garden path now and although she is a deceitful piece of work, you need to make things clear to her now, or everything is going to get worse.
As a PP mentioned, she doesn't seem too bothered about you seeing her less so it may well be that she won't be too bothered about you ending it.
Attend the scans with her IF she wants you to, otherwise be available to help with buying baby stuff, sorting out housing/room for baby. Then wait for it to arrive and make appropriate maintenance payments and agree a contact schedule between the two of you.
Please don't stay with her out of some misguided desire to "save" the baby from having a "broken" home. If you're there onyl for that reason, then the home is already broken. Far, far better for a child to have two separated but happy and healthy parents, than to be stuck in the middle of a toxic marriage full of resentment and bitterness.
I'm sure you've heard enough about condoms to never make this mistake again, so I'll hold me water on that :)