He's trying to do the responsible thing now.

He shouldn't have done a lot of things, but running away after what he's done? No, I don't think that will help him. He wants to be a better dad than his dad.

He can go for long walks, find a hobby, or side hustle, that gets him outside the house, for a few hours at a time. He can confront his fiance about the lieing. He can tell her that he wasn't ready for this and that he's going to need her to sign a pre nuptial agreement.

She is capable of extreme deception, but ultimately, you should never ejaculate into the vagina of any woman you don't plan to father a child with because you are culpable if it leads to a child. You are culpable for what is growing inside of her.

Go to therapy, exercise, do things that fill you up because you're going to want to have those healthy habits to support you in the future.

I'm glad you're venting. I'm available to talk if you need support. I hope that you get the resources you need to make the most of this situation.