First you described the partners need for sex as sexual assault. Without even the consideration that he may just have a high libido like OP said.

And then you said that it sounds excessive without knowing much about their relationship. OP's only problem with their partners high libido is that it leaves them sore.

And lastly, you said that the partner is the one that needs therapy. Again, another assumption that only one person needs therapy. If you're going to assume someone needs therapy, why not assume the couple needs therapy?

OP came to the internet for help instead of seeking professional help. If anyone needs therapy. it's someone that goes to the internet instead of going to a professional first.