It takes time and patience to expand a vagina! And, it has to be done a little bit at a time. My wife was post menopausal when we first got together, had not had sex for 27 years, and her vagina had shrunk so much I could only get the tip of one finger in her. So, that night I gave her the first orgasm she ever had from oral, and she loved it. For the past two years we have worked twice a week stretching her vagina, first with my finger, then graduated dildos, and now with small softer type cock sized dildos. Last week she started to be able to take, and enjoy, a 1-1/8' diameter dildo. We have several more to go before she can take my 1-1/2" diameter cock, but we are close. It is about 5 inches in circumference.
The key is every time have him give you an orgasm from oral and/or dildo. That relaxes the pelvic muscles and helps them stretch without pain.
Good luck!