Lasting longer

My boyfriend is a bit new to sex and all that (I took his virginity and I’m the only person he’s had any sexual contact with). I love him dearly and he’s the sweetest guy. Since he’s still figuring out things, I usually end up on top, which I don’t mind as much since I’m getting better at it. Problem is that since I got better at riding him, he now finishes much sooner and I end up unsatisfied and a bit frustrated. We’ve only been able to go one round at a time because he gets too sensitive and get hard again. I know it may take time to build his stamina, but I was hoping to get some advice on how to help him last longer so I can be satisfied too? And if anyone has any secrets to help him go more rounds, that would be fabulous as well. Thank you!