im so genuinely sorry this happened to you! the first thing to do is to calm yourself down. go talk to someone IRL if you can. a friend you trust or your T. be very very gentle with yourself and try to listen to the rational part of your brain that is telling you this is NOT YOUR FAULT, you DID NOT invite it and YOU HAVE NO NEED TO BE ASHAMED. this is not even about you. its about that creep who has no sense of decency and respect. you were caught unawares and triggered so its perfectly understandable it took you time to react and in fact well done for acting when you did to stop him.
it is most definately considered sexual harassment but pixie is right. making a decision as to what to do about the guy is not the priority right now and not necessarily a good idea at all until you start to feel better yourself. i dont know your husband so i cant say whether you should tell him or not but i do know that is in no way considered cheating or being disloyal to him AT ALL.
i wish so much these sort of things didnt happen to people. im so so sorry. my thoughts are with you. please do talk to someone IRL and dont try to deal with this all by yourself ok?
take good care of you,
biiv