idk what's wrong...Help

My SO can't seem to stay hard for so long and he tries to get it hard, but it doesn't and I could tell he gets hurt/disappointed. Is it like something medical or am not doing something right? Is it normal?

It sucks because it's like I'm barely getting into the mood and bam it just goes down. Now I rather not even have sex, but i feel like by doing that I'm hurting my SO.