Please please help me.

Okay. Ladies please I need all the help I can get. My boyfriend is having a hard time keeping a hard on. I'm starting to think he may have some sort of problem below the belt. Lemme explain his situations.  To start. I'm the first woman he's been with in two years. He beats off all the time and gets off everytime. But when it comes to us, he can get hard quick and it'll last maybe 20-30 mins but then he'll go soft.  Even if we're having sex, he can't get off either. Unless he's beating off. It's starting to make me feel like it's my fault. He swears it isn't. He says" he's not used to vein with a female. Especially one as beautiful as me. I'm to pretty to be with him (which isn't true)  but then today we had sex. And he lost it after about a half hour, and I tried again like 26 mins later and he couldn't get fully hard. I don't understand how he doesn't have a problem getting hard and beating off. But he can't keep a hard on while having sex and get off. And I know that I am not bad in bed.  Please help and send some advice my way