Nothing in your description mentions "showering". I have a feeling that being clean is not the issue.
Enjoying time in the hot tub is not the issue either. If you had been invited and were in the guys tub, would you have complained?
And you don't know if anything happened unless he told you about how many times he got fucked. Since you said that you imagined that he got laid, I assume that he didnt tell you.
It is possible that nothing happened, his penis stayed in his pants and he is just driving you crazy. Successfully. Although he obviously hoped that something would happen. If he was just interested in getting screwed he could have invited you, or stayed home and fucked you all weekend.
Please quit worrying about this. You are not important in his life. He screws you when it is convenient for him while he looks for other women. If you don't like that, just quit being the easy piece and move on.