I find it's difficult getting involved when the emotional ties, from a previous relationship weren't completely severed. Therein lies your concerns. I like the idea, of give him time, to finish the severing of that emotional connection.
Better to know now, than having a bombshell dropped on you, several months from now.
Ideally, partners entering new relationships free and clear, pasts resolved is ideal. Yet, we don't seem to live in an ideal world.

Keep us posted.