Did i meet a weird couple? or am i just lost? gay and lesbians?

So i met a guy this weekend. He's gay but he is currently in a relationship with a girl. Its really weird to me because she is gay as well. So i asked him how do they have sex. He said that she get a strap on and tops him. I kinda of makes sense.. but its just a little weird. He's masculine and look like she is slightly tomboyish. My question is does any body else think that its a weird or should i say different? Has anyone been in a relationship like that? Is this a popular thing?