My heart's breaking :'( i like my best friend but he likes my best friend :@?

Next time you speak to Greg, if he talks about her all the time just ask him if you can talk about something else. Tell them both the truth that you don't like being in the position that they are putting you in and refuse to p messages between them. Let them sort themselves out. If you want to you could tell Greg how you feel and that it bothers you how she treats him.