My bf can’t get hard

We’ve been together for 6 months now and have had sex plenty of times. I remember though when we were barely starting he’d get really nervous and cum before anything happened. The first time I invited him to my house he couldn’t get hard because he said he was nervous. But after a couple of weeks after that we had normal sex. Until recently it’s happened twice. He can’t get hard. I suck on his dick until it gets hard and we put it in quickly. That seems to be the only solution for that. Idk why this happens if he gets hard any other day when he’s with me. Like we’ll be at school and he’ll just hug me and he’ll get aroused. He’s starting to get really worried. And I try to comfort him when it happens because he gets mad and embarrassed. But I’d like to know what y’all think?