Unless you take the Donner Cut of Superman II into account, in which Supes and Lois do the deed before he loses his powers.
Which is just insane. If he doesn't have to choose between superpowers and sex with his girlfriend, then why the hell would he give them up?
Well, the Donner Cut is pretty bad.
But in any event, Superman didn't get rid of his powers to bang Lois. He did it to be with Lois completely. As Superman, his duties and responsibilities would require him to be elsewhere a good portion of the time and he wouldn't be able to be in a strong, committed relationship.