What would you think if your girlfriend came on and posted something like this:
"I really want to see my boyfriend get fucked in the ass by an enormous black cock while another one fucks his mouth and cums down his throat. It's a massive fantasy of mine."
I don't think you'd like her fantasy and I bet you'd feel differently about her if you knew she wanted to subject you to that. I bet she fantasizes about finding a boyfriend who asks her what HER desires are and doing what he can to make HER dreams come true.