Is she cheating on with gay friend?

My girlfriend talks with her guy friend alot. On the phone, facebook, and at work. She said oh dont worry he's gay. She said its one of her best friends. So I kinda believed her. Then I found out she goes out to eat with him, shes been over to his apartment before. I recently read an old facebook message that she sent him that said "Lets make a date" and I brought it up to her and she said that she wasnt asking him out on a date it was just an expression. I told her how bad it makes me feel that you talk with him and she said he's gay dont worry. I asked her if he ever told you he was gay and she said no but she seen his boyfriend before. Yesterday was his birthday and she spent two hrs decorating his classroom the night before, she got him a present, and she texted him at 6:50 in the morning to be the first person to wish him Happy Birthday. I dont believe my girlfriend at all and I cant stop thinking about this. What do you ladies think? Is she cheating on me, is she being disrespectful, is this guy gay? Do you think she loves me? Thank you and be honest Please!

... Ask to meet him (check out his "gaydar" for yourself). If she doesn't want you to meet him then you may have something to worry about. Have you spoken to her and told her how her one-on-one date-like activities have you concerned about things?