Why are open relationships seemingly common within the gay community?

Hi, First of all I would like to state that I by no means have a problem with people who choose this type of relationship however as somebody that doesn't actually know gay people in real life, but uses the internet a lot I am curious as to how common open relationships really are in the gay community.I am a bit of a romantic and the idea of a guy being in a relationship with me and doing stuff with other guys would really hurt me but it seems so common that im worried about dating anyone at my age (22) because they might just want to fool around behind my back if i didn't agree to a open relationship.To the people in a open relationship what made you want to have a open relationship instead of just the 2 of you? I cant help but think i would get jealous but maybe I am just a insecure person.