I think it’s perfectly fine to go back to exes or sleep with them or dating them after divorce. There are no rules on what you can or can’t do.

The only concern is that you only sleep with or even hang out with ex when there are no other men available. When jay was hanging out with you more you were very into him like having butterflies etc you didn’t think of ex in that way, didn’t think of him as cuddle or soothing buddy. When jay pulled off a bit and taking it slow, now ex is needed for soothing and all of a sudden all this caring for ex.

It’s like you had to fill the space with a man. And if a man of your choice isn't there then ex will suffice. I think neither jay nor ex are good choices here at all. It’s better not to have any man right now. Imho. It only causes more stress. Or if you really want to find a man in a hurry, I’d focus on looking for better quality men.

Is being with your ex make you happy? If yes then maybe that’s the way to go.