When I go swimming I like to take my time getting into the pool. I'll dangle my feet for a while, then step in to my hips, and keep taking very slow steps until I'm fully immersed. It helps me to feel comfortable at each step and get acclimated before going in a little deeper. If I just jumped right into the deep end I wouldn't know until it was too late if the water was too cold for my liking, and once in there's nothing I can do except deal with it or drag myself out of the pool and wait until I can dry off and feel comfortable again.
I see no reason for you to take a blind leap of faith into the pool. You said you're not even sure how you feel about him so take things slow. You two can always start dating if you'd like. Build your relationship back slowly. He can certainly show he can be a good husband, father, person without moving back in. Let him EARN the right to be a full-time part of your and your kids life. Time will reveal much and I think when the time is right for him to move back in you will just know it (or not). The kids deserve for you to err on the side of caution.
JMHO