Even without factoring gays in, even straight people have pressure and wind up in sham marriages. I mean, it's no doubt people confuse lust with love, and wind up rushing into relationships... then of course women who feel the pressure that if they don't, they;ll be miserable and alone and their friends will all laugh at them behind their backs.
We have to break free from society's self inflicted uniformity, or at least learn to examine it.
To be fair, a lot of couples go through times they do not see coming at all... and a lot of them find themselves married to people who change for the worse. Sometimes either the husband or wife becomes gradually abusive. If something terrible happens in a marriage, it IS a just cause for divorce.