This might not help at all but i had the same problem only after a while discovered it was because of an allergy yo latex in condoms, causing down there to swell and feel really tight!
Hi,
You should try more foreplay just before he tries to penetrate; foreplay will usually help naturally stimulate vaginal fluid, that relieves dryness during sex. If that doesn't seem to work, use a water based lubricant just before penetration. Meanwhile, keep reminding him to go slowly, and you should see an improvement soon :)
Good Luck