19 & trouble getting hard

I love my bf and have been w him 2 years. My sex drive is rlly high but I find my bf sometimes has trouble getting/ staying hard. We do have decent sex but when he has trouble staying hard it makes me worry it’s me. Like he’s tired of me or doesn’t find me attractive. He says it’s not but I worry. He doesn’t go soft all the time but I just feel like 19 year olds shouldn’t rlly have trouble in that area? Every time it happens he always has an excuse for it. Like I had to pee or he was thinking of something and he went soft. What do I do.