Blowjob- feeling discouraged

I’ve been with my bf for four years. Ik he loves me and blowjobs aren’t a big deal but I still just cannot get it right. He says he can feel my bottom teeth and I keep stopping. He’s okay with it and doesn’t mind, that was just the feedback I asked for. I feel like I’m opening my mouth as wide as I can, I have TMJ so it’s really hard for me. My jaw gets tired really easily. I just feel super discouraged and awful. I wish I can give him an official good blowjob and actually succeed for once. I genuinely don’t know what to do. I have tried every tip I’ve read and I just cannot get it right.