Questions About Aliens

Hey recently my sims met this really great guy and they really hit it off (he's really fun and sweet) but I found out he was an alien and I don't know how I feel since he is a real catch and my sim really likes him so I'd hate for them to break up. So I have some questions to make a proper choice.

Even if he stays in disguise will she give birth to an alien?

If she does when can the kid put on a disguise?

Can he visit his home planet easily?

Does this effect gameplay much?

How do half human half alien sims turn out?