Regarding the Original Post:
It is very common, in Both Gay men and Heterosexual couples too. sometimes the Lust and sex fade in a relationship. I have a number of (elder) gay friend-couples who no longer have sex with each other, and that is for various reasons. For some it is due to one or both having medical issues. For others, its just that they love each other and will stay with each other for emotional reasons, but the spark of sexual intimacy is gone.
For me, I can say the following. I am essentially sexually Polyamorous for the physical act of sex, however I make commitments based on emotional connection to others. I do not expect the men that I get with to stay sexually faithful to me alone. I do however expect them to know where (home) is, and that I would be there for them. If for whatever reason the man I am with feels more strongly for someone than me, I would hope that he would tell me. To me, a relationship based in Monogamy, should not be a sexual prison. You can love and be faithful to someone yet still be physically polyamorous sexually speaking, with others. If I got sick, and I was unable to perform for my partner, I would allow him the freedon to go play with others, because I would want him to be happy, and have a need that he would want met, be met by someone else. That, would make me happy, that although I was not able to meet his need, that he had the freedom to go get it from someone else who could. I honestly feel that there is no reason there should be Bed-death. . at all. . but that is my opinion.