1.) It might be interesting, but the gay community isn't, as a group, going to answer you--individuals maybe--and their experiences would be anecdotal at best.
2.) Failure to achieve and sustain a long-term relationship is problematic.
a.) first, the fact that a long-term relationship doesn't last doesn't necessarily constitute 'failure'.
b.) second, I think you need to quality 'sexual activity': do you mean 'a lot' 'some' 'excessive'?
c.) third, the argument used that sexual fidelity increases the chances of a relationship lasting a long time has been advanced by
conservative christians as a reason to abstain from premarital sex for straight people: if you haven't had enough sexual experience to distinguish between bad, middling, good, and great sex, a couple is probably not going to be dissatisfied with what each partner gets from the other. Ugh! Another ignorance = bliss equation.
d.) fourth, it's not just gays: the rate of divorce and multiple serial marriages among straight folks may in part indicate that sexual dissatisfaction or unmet sexual needs of an individual and/or the desire to look for something better is not limited to gays. Also, it may not just be sex that accounts for plural partners.
But what I find disturbing is your word choice 'failure'. It's as though you are trying to be normative and insist that a long-term relationship is or should be the desideratum of
everyone. Clearly that's not so.
I've had a monogamous relationship with the same man for almost forty years, but I sure as hell am not going to say that everybody else should do as I do. I would never generalize from my own experience to others. I have never had sex with another man since entering this relationship, but I have considered murder...
I have friends (gay, straight, bisexual, and whatever else there is) that have or have had multiple relationships and are very happy with that. The women that I know, gay and straight, are pretty open about having had multiple sexual partners with whom the sexual satisfaction was certainly not equal across all their partners--same is true of the gay guys. I also know happy straight and gay people who have only had one partner. Hell, I even know singletons (people who don't have interpersonal sex at all) that are happy, fulfilled individuals. I know long-termers (lifers) who say sex is not an important factor and never was.
Just because a gay man (or a straight one) is/has been sexually active with, well, maybe more than ten fingers worth, doesn't make him a 'libertine' or 'promiscuous'. I've had a lot of straight friends (single and married) who say 'Well, I'm a hound (and you know what that means), and I think no less of them. And I don't think that a woman who like sex with lots of men is a human luge.
Your post is disturbing to me because it's one in a string where you make value judgments about others who aren't like you.