Help!

So my boyfriend is starting to get frustrated and discouraged whenever we have sex because I don't orgasm every time. He's recently discovered that I'm not wet all the time even though I tell him that I'm horny. He's really starting to take things personally even though I've explained that I can't orgasm every time and that I love having sex with him. Any ideas on how to help his ego? And how to relax more in bed? Because all of this is adding so much pressure!