I can understand you wanting to leave since you live with your exes parents. They must be nice people tho to not mind you living there even tho your not married to their son anymore? Maybe they won't freak when thy find out and you will have some time to find a place. In the meantime you can help your new man find a place and when you're able to you can move in too. How far along are you?
Tell your guy to hurry up. This is not something to be casual about, it's time to move your kids and be with him if that is what you plan to do. Don't let your kids associate your pregnancy with getting thrown out by your ex's parents. If you go to them with dignity and say you are moving because you found out you are pregnant, then it's their option to tell you it doesn't matter to them and you can stay, but at least you have given them the graceful out.