Why not ask the man in question? Every man is different (the same way that every woman is different). I have had times where I have not finished (for one reason or the other).
Speaking for myself (and that is all I can do)... if I get an erection with you, that is a pretty good sign that I find you attractive. Of course, if I didn't find you attractive, I wouldn't be in bed with you in the first place.
The best sexual relationships are based on communication and trust. If you find yourself with a man who doesn't ejaculate, talk to him about it and trust what he says.