There's no hard data or surveys available that provide reliable figures for what percentage of the sexually active gay population are in partnerships that would fit the criteria for the term 'relationship' (when compared to the heterosexual model) but empirical evidence of various sorts as well as the high rate of partner turnover in that community compared to the relative paucity of opposite-gender churn suggests LTRs are the exception, not the rule. Do you know gay people in relationships? Yes, you do. Are they representative of gays in general? Very likely not. For one thing, gay marriage rates have hardly skyrocketed in the past 3 years of legality. If you think about it, the venues and resources available to men for the purpose of meeting are practically geared towards the one-time hookup business model. There just doesn't seem to be the desire or the tools available for them to meet in the way some straight people do through mutual friends, conventional dating sites, and work (since being openly gay or approaching men whose orientation is unknownto you are is still generally not the norm).
I'm aware that much of my family is exceptional when it comes to maintaining their marriages. I also know regardless if their relationships are gay or straight, this is not the norm. Forty to fifty percent of married couples in the United States divorce. The divorce rate for subsequent marriages is even higher. If these stats are correct, more than fifty percent of of the population get's divorced at least once.
One family exception is my sister, who is straight. She has been married five times, plus she's had additional relationships, which did not result in marriage. She is currently single and looking.
I may not be the norm, but not because of the reason you give. I've only had one marriage and no other serious relationships. My situation is probably not even in the statistical mix or at least it is a very tiny minority. Unlike my sister, I'm not looking for another relationship or marriage. Just so you know. I have never instigated a hookup and definitely not one with someone who's orientation is unknown to me.