Stop dating separated man
Most likely what a guy did to his ex-wife, he will do to his new girlfriend or future wife, if he remarries.
My sister is dealing with a divorced guy too and she is just going by what he tells her went wrong with his ex-wife.
Tell him that if/when he's spent some time processing and is ready to date seriously again, he can give you a call.
If you're still single, you'll consider giving it another go.
Consequently, many jump into relationships before they're truly ready, often without even realizing it.
This guy needs to take some time off, evaluate where he is, get his head in a better place as a single guy and then when he's truly READY to be in a relationship, start pursuing a relationship once again.
If he keeps quasi-dating you while offering "nothing serious" he will never get the space and distance needed to clear his head and be ready to be a real partner.
Just don't set yourself up to be hurt by investing more in it that he can even contemplate giving you right now.
What everyone is telling you (to beware) is probably correct. I married the first woman I dated after my divorce and never had any interest in anyone else for as long as she lived.
This guy is going to go through more waves of whatever it takes for him to get over his ex-wife, learn to stand on his own again emotionally, and be ready for a relationship.