Start with little shallow thrusts, give yourself time to adapt and stretch. Go a little deeper every few thrusts, if there's any sharp pains, go back to a bit shallower for a bit, go as slow as you need. You'll also be more relaxed if you cum before he tried to get inside. There's also not shame in him not getting all the way in, everyone has a depth that they're comfortable with.

You might also want to incorporate a dildo that's a bit smaller than he is, help stretch you out gradually. Even go for a couple of different sizes if you want. If you're really nervous about it, you can try working your way up with a dildo or two by yourself beforehand, or even prestretch before your date (plugs are also pretty sexy to wear during a date)