Quit trying to lure him back. You can't miss what is always in front of you.
Work on yourself, become the best option. You can only do this work when you stop focusing on H and turn it towards you.
Your H is viewing you using the kids as pressure. Pressure equals running behavior.
You're it 2. You're going to have to fill in for a while with your kids in your H's place. You can't force him to parent them.
Step up to the plate 2, it sucks, but you're it for right now.
As far as GALing is concerned, I agree, it would be harder when you're pregnant. Now would be the time to search out some single mother's groups in your area and start making friends. You really could help each other out by trading off babysitting time.
