I have a secret I've been keeping for years now. I have a friend I have known for a long time. His current GF he has been with off and on for 3-4 years now.

I am the only one that knows this and he doesn't know I know this, but he is gay. I found out through an ex gf that thought I should know, after one of her gay friends hooked up with him. I found out about a year before he broke up with his last GF. There are a lot of details that would be helpful but that I cannot get into.

Here is the problem. He is hooking up with guys on the side, and that isn't cool. I've been keeping this secret for so long and I feel like his GF should know. She will be angry, but I also worry about him being outted. If the truth comes out it will be hard for both of them to take.

I want to do the right thing but I don't know what that is in this situation. I've thought about talking to him, talking to her, talking to her best friend, and it doesn't work out well. It is a fragile situation and is going to be life changing for those involved.

What's the right thing to do?