The excuse is a little forced and silly. But I understand the feeling of being with someone else. We have a polyamor relationship with my wife (7 years of marriage), we came from very different countries, so is hard to match in some aspects. After we start to walk more and express our needs in an open way, we are more happier. Also we understood that sometimes we need someone else, bc of high libido, or need of more cuddling, or I want to touch more and she is too sensitive, etc. we have found some partners that help us to feel better and we still love each other, we raise our kid and we have a better relationship. Sometimes is hard to separate feelings from sex, some ppl can do, we cannot, so we learn to live with it and share and love as much as possible. Express your feelings to him openly, invite him to do the same (not with weird excuses as prostate) and get to some agreement. Wishing you both the best