I'm not cumming from sex every time. How do I tell my bf to help me our after he cums?

Okay so basically when my boyfriend and I have sex, I don't always cum. Honestly, it's not very often that I do tbh. But I am a strong beliver of how both people engaging in sex should cum every time, even if it's after sex has finished. He will sometimes help me out after he cums but the point is.. it's not EVERY time. So he'll cum and then just lie there for awhile and then sex is just done. So the issue that has formed here is that, since we've been having sex for a couple years now, we've become used to the fact that basically sex is usually always over after he cums, which is not fair at all. I have talked to him about this once before and he seemed kind of irritated almost, idk if it's because he thinks he's doing something wrong, but basically I just wanna know how I can bring this up again and what I should say???