I agree with fini on working your were there and not rushing anything.
Speaking from the side of someone who has been sexually harassed, I would appreciate an apology from that person if it is respectful, sincere and if it feels like he realised what incredible harm he has done. Something that I would find unacceptable in the apology would be if it seems like he's just pitying me or feeling sorry for himself, or just wants to know that he's forgiven.
The apology shouldn't primarily be about you lightening your bad conscience but you wanting to help the other person.
However, that's my opinion.