Musician boyfriend always wants attention

So, my boyfriend and I are both musicians and we get along really well, but there is one thing that is really bothering me. He is always wanting to steal the limelight whenever I perform in public. I told him I want to focus on my own music because we always performed together. And the performance are always around what he wants to do, he has to play guitar for himself because otherwise he can't keep beat. I have to improvise to keep in time with him when he plays to his own rhythm. I can keep timing to most beats, but he changes every song to his own rhythm.

Anyway, I wrote some songs recently and the best song on the album he says he wants to play the guitar for me while I sing. I told him it was not a good idea because the guitar helps me keep the rhythm of the song (and his rhythm is not the best for my style), and he got upset that I wouldn't want him playing the guitar.

The last few times I've got up on stage to do my own thing, he has jumped up on stage with me, and then completely changed the songs I was going to sing. He has his own style and so do I, so I don't know why he is always wanting to get in the way of my performances. I got up to sing karaoke just recently and without asking, he picked up another microphone and started singing really badly along to the song with words he was just making up. Everyone was put off and it was really embarrassing.

He writes his own songs, and he tried to change the words to a song I wrote and I told him I liked the way the song was and didn't want it changed. Everytime I get a gig, he acts jealous and complains about the people offering me the gig. We get a regular gig together every month and everytime, he plays for longer than me so I keep my set short. I am really sick of not being able to shine in the shadow of my boyfriend who wants all the attention.

I have told him over and over again that I just want to perform solo and he keeps jumping in. I don't know what to say to him to make him stop, so I can maybe get noticed and have a career. He is getting in the way of my ambitions, but everything else is perfect in the relationship. What do I say to him?