One difference IME is that everyone I know who went down the open-relationship did it to try and solve their current relationship problems. No gay person I know decided to be gay to try and solve their problems.
> No gay person I know decided to be gay to try and solve their problems.
I suppose problems could arise by trying not to be gay in a time/place where it's been deemed abnormal or immoral, hence just being the gay person you are would solve some of those problems. If you're incapable of being faithful in a monogamous relationship, that's a real concern and a huge red flag, but one way to solve ot in the near-term would be to stop trying monogamous relationships, whether or not it's the cause or effect of it not working. Suppose you eventually go to therapy and realize you were habitually cheating for some other reason, problem is still mitigated somewhat by avoiding the context where those problems arise, much like avoiding skid row when drug addiction causes you problems.