Is your boyfriend a gynecologist? Go see your ob-gyn and get an exam and ask if your vagina is unusually short or in some other way unusually shaped that would make your (non-medically-trained boyfriend who evidently does not have experience with very many women) call it "shallow."
Most vaginas are proportional to the woman's body height, I'm 5'6" and I think my first gyn told me my vagina is something like 5 or 6 inches long. She said that was normal for how tall I am. If I were to have had a lover whose penis was longer than that, his penis would have bonked my cervix during sex and the base would not have been inside my vagina. Since it is not comfortable to have your cervix bonked, I might have said to him not to do it. If he had then come up with the snippy or defensive-sounding comment that this was a problem and that the "problem" was my vagina length not his penis length or his inability to stop pounding my cervix, it would make me wonder what else he was going to start blaming me for that was not a matter of being a "bad thing" but just was the way things were.
If your doc tells you that your vagina is perfectly normal for your height, tell your boyfriend to go soak his head.