Too insecure for sex

So it’s my birthday today, and my friends and boyfriend are coming over for a sleepover. I love my boyfriend to bits but I just can’t relax when I’m naked around him, or anyone for that matter, so I keep avoiding it. He’s going to want to go for it tonight and I do too, but I don’t know how to get myself to realise that it’s okay. I haven’t eaten in over 24 hours but still feel disgusting. Any advice?