You're forgetting about the laws of agency and the post modern condition.
It's funny, because my mums friend the other day said "You have to remember that all the people at the party i went to the other week were all hilarious, because they were all gay & lesbian, so by their very nature they are funny & happy people who like having a joke!"
Both you and her are incorrect.
By post modernism, you cannot define these people in a particular way.
By laws of agency, an individuals characteristics overide any group characteristics which may exist.
Its obvious that you label these people as GAY and then find them to be a particular type of person, and somehow relate this back to the fact that they are gay, rather than viewing them as being humans who just-so-happen to possess a certain character trait. When you label someone as "GAY" every time you look at them you view them in a certain way or get a certain feeling about them. This is all just your imagination.
Somehow sleeping with someone of the same sex makes you a "backstabbing, gossiping, untrustworthy" person.