Feeling pretty down :(

So background...Me and my SO have sex every time we see each other (which is only 2-3 times per week because of our work schedules). The sex is really good to me, but I can't help but feel like it isn't all that great for him :(. Like tonight...he comes 99.9% of the time. But there are some nights where he can't. When he doesn't, I internalize it, I feel like it's my fault or that I'm inadequate, and it makes me feel pretty shitty about myself. I might be making a big deal over tonight (he was hot, tired, sleepy, and has to wake up at 3am for work), but I still feel bad.

I just feel like I'm not pleasing him. When I get on top or give him head, I lose courage quickly :( I'll keep going and he says he likes it...but I still feel inadequate. It's causing me to have some serious issues with the way I view my sexuality, attractiveness, etc.

I guess what I'm wondering is, can anyone relate? Is there anything I can do to make myself feel better? Might it be in my head? Or do I need to work harder at it?