I feel like a total failure as a wife

I’m 24 weeks pregnant and sex is very painful so it doesn’t happen often around here and when I does it’s boring for him. I caught him getting off to porn which I don’t care about at all I just feel terrible that he needs to watch that instead of me. Anyways, I decided I would just try and have great sex tonight. It started off fine but 5 minutes in he loses his erection and can’t get it back. So I told him I just didn’t want to have try and have sex anymore and went to the bathroom and cried for awhile. I can’t even keep my husband turned on anymore. I feel totally disgusted with myself. I’m feeling worthless. I’m not good for anything.