You're still young an attractive. The stage has been set. He's always gonna be linked with this girl, if the child is his. And if the child is his, the child is always gonna remind everyone of the situation.

I'd hit the road, peacefully and amicably, for your own sake. I mean, get all ya can, but don't waste to much more of your time. (I'm in my early 40's too, and time is on my mind more than ever. Time for you to go and do your thing while you're still young enough to want to, imo ) It's not worth any more energy to make it work. You need that energy to move on, for you.

And an affair is one thing. A live child is another. They're not equitable scenarios. And I'd say that to anyone that gives you shit for leaving.