How will you feel if he says "no," that he can't/won't continue to have contact with you after your professional relationship ends?

I think your instincts are right that he has crossed some boundaries. And it's possible that he might be fine with being friends. But I think it's also possible that you bringing it up might make him realize that he shouldn't have spent so much time with you and that revelation might make him pull away. That wouldn't be your fault of course, but I can see that it might hurt.

It's obviously your decision if you think the risk is worth the possible reward, but I would suggest making sure you have some supports in place just in case you need it.