Can a guy ever “go in too far” and cause a very hurtful pain?
No. Most women have vaginas that are about three to seven inches long, but they can stretch to be even longer during vaginal intercourse. It’s true that some penises are too big to fit comfortably into a vagina. But a woman’s vagina ends at the base of her cervix, which connects the vagina to the uterus, and a penis can’t enter the cervix.
Some people enjoy deep penetration during sex, and some people don’t. Sex can be a lot about trial and error — figuring out what works for you and what doesn’t, what you find pleasurable and what you don’t like. It’s really important for you and your partner to communicate about your preferences and for you to tell your partner if anything hurts — sex that’s uncomfortable for you should not continue.