I don't want to go to a bar to hear my boyfriend practice his instrument
Why don't you want to go hear him play?
I have a headache and I'm not in a mood to listen to music, I also don't think he is good.
It can be awful to listen to bad music when you have a headache but your boyfriend needs your support. You could go for a little while so that he knows you care.
I don't know why he is so desperate to have people listen to his playing. He should just work on his skill at home.
They sound like they just want support. Have you tried being honest about how you think they play? You could offer him advice on his strong and weak points.