I'm with Iris. You made a child with your wife- do you want to be an every other weekend dad, or a real and present one?

Not surprising that you're suspicious of your gf, considering how the two of you got together. Second marriages fail even more than first ones, for all of the reasons you listed, especially ill feelings over the step kids.

I hope this doesn't sound too harsh. It just bugs me when people give in to their own selfish needs/wants without considering the needs or wants of their own children.

Good luck to you whatever you choose.