It's really fun sucking the bull's cock, especially when your gf's watching. I also think it's important too because of the message. Like the first time my girlfriend watched me suck the guy she was dating made things REALLY clear.I was jealous b/c she was referring to him as her bf, and I accidentally made a smart ass comment that made them both mad. Basically things ended with his dick in my mouth while I apologized for being "disrespectful". My gf was really surprised and laughing a lot, and it was humiliating. I loved it, and that it happened.
It was really important though b/c I didn't feel jealous anymore. Afterwards I went down on her and we talked about how amazing his dick was and about how much bigger he was than me. She explained why it was important that I referred to him as her bf and why he got to have sex with her more than me.