Boyfriend doesn’t last

My boyfriend is 16 and I am 17 and we’ve been having sex since August. At first he would last like 5 mins but for some reason lately he barely lasts a couple minutes... I don’t mind it that much but it’s gotten to the point where he won’t have sex with me anymore because he’s embarrassed of how fast he comes. He’ll even come twice before we get to the sex and still won’t last. Any tips?