(NSFW) How do I make my fiance feel better after he couldn't get it up?

Okay, well, I’m 22, and my fiance Mikey, is 26, and we just got engaged a couple of weeks ago. Mikey is the most important thing in my life, and I love him so much. He’s the sweetest, kindest, most gentle and understanding person I’ve ever met, so of course, I’m extremely excited to marry him. :) Well I moved in with Mikey about a year and a half ago, as well. I don’t want to go too in-depth here, but normally, Mikey and I have a great sex life. He was my first and will be my only, and he only had sex a couple of times years ago with an ex girlfriend. He’s wonderful and sexy and he’s always so attentive to me; he never has a selfish moment and he’s never disappointed me in any way.

Well, Wednesday night, around 6 pm, I started getting really… in the mood. Mikey had to work late, and he came home around 7. I wanted him so badly at that point, that I practically pounced on him as he came through the door. We started making out, and I could tell he was into it. We went into the bedroom and continued everything, but he couldn’t get it up. This has never happened to him, ever, and we tried for quite a while, but still nothing. I could tell he was embarrassed the whole time, and kept apologizing. I told him it was fine, and I went to give him a kiss, but he sort of pulled away and just kept muttering things to himself like “I don’t understand why this happened.” He’s been very quiet since then, and I keep asking him if he’s alright, and he just says “I’m fine, baby, don’t worry.” He’s been shy about anything to do with intimacy since then, too, and he seems really embarrassed every time I ask him if he’s okay. What’s going on? How can i make him feel better? I don’t care that he had a problem one time getting it up, I just want him to stop feeling embarrassed about it. Advice?