My boyfriend can't last for more than a minute?

So I'm not writing this to be condescending at all, but my boyfriend seriously can't last for more than a minute and a half tops. He's fully aware of this and I know he's self conscious about it so I always try to reassure him. I can tell that he tries to pace himself while we're having sex (he'll thrust hard for a few seconds and then slow down, continuing that pattern). We're both 18 and have had sex 10-15 times since October (we're an hour long distance so it's different).  Sex feels great but I can't get anywhere in a minute and a half... we experiment with different positions and everything but he always lasts the same amount of time. He lasts a bit longer if I blow him/give him a handjob. Any advice? I've never came with him because I never get the chance to, but it's not really a big deal to me.