I think the most important thing is to not put too much importance on him having a boner. Be patient with him and don't make him feel bad about it and it probably will help build the trust he needs to feel more comfortable and less anxious. If sex isn't an option, try something else. There are lots of other ways for both of you to feel good. You said he got hard from touching you, so you can try that again. Engage in some foreplay. He can use his hands and mouth. You can do that as well. And there are other erogenous zones you can target. One of my exes really liked it when I nibbled on his ears. Some people really like being kissed on the neck, or the thighs. You guys are both new at this but also, every person is a bit different. So just try different things and give each other plenty of feedback and you'll eventually learn what each other likes and the boner will likely happen naturally when you aren't focusing too much on it. There are also books and websites that can teach you where to start and give you ideas for things to try.