It's the usual blinkered vision that is always used to justify putting a group down: scream about about the bad things and completely ignore the good.
Yes, there are gay men who have many, many sexual partners.
Yes, there are straight men who have many, many sexual partners.
Yes, there are many straight couples who are faithful.
Yes, there are many gay couples who are faithful.
Yes, gay couples break apart.
Yes, straight couples break apart.
Don't forget though, society puts a great deal of effort into keeping straight couples together: marriage, tax benefits, etc. The general reaction to a straight couple showing affection (e.g., holding hands): "Isn't that sweet".
It also puts a great deal of effort into forcing gay couples apart: keep yourselves hidden, no marriage, no tax benefits. General reaction to a
gay couple showing any affection (e.g., holding hands): "That's disgusting".
What do you expect!
I find it encouraging that a great many gay couples do manage to overcome these tremendous negative pressures and lead good, satisfying, and productive lives together. The sad part is that many do so in secret - helping to prolong the myth that gay relationships are shallow and cannot last.