Re: If you need more exact instructions,

While you maintain that loving sex is no more vigorous or uncontrolled than masturbation, you also say that the penis goes into the vagina as far as you can, with due comfort to both parties.
It is very easy to masturbate comfortably by keeping the frenulum free from uncomfortable tension by keeping the foreskin over (i.e. predominantly covering) the glans. If, as you say, the penis goes into the vagina as far as is comfortable, that, with a short and slender frenulum, is about the length of the glans, i.e. about an inch/inch and half. That is not going to achieve a great deal, so one slowly ventures a little deeper, if one can without it hurting. What happens then? Withdraws a little and carefully ventures forward again. What happens then? You realise that this is nothing like masturbation because your foreskin is retracting which puts the frenulum under tension which up to that point you had been able to protect by not retracting the foreskin. You do your best despite the pain, and end up with a torn frenulum, with either a little or a lot of blood (depending on which blood vessels are torn in the process), or some bruising.
Personally, I would have preferred to have avoided this pain and difficulty and would have preferred not to have then been told by a urologist that circumcision should be considered (he gave no logical explanation; this was in 1984, and was standard shocking and terrifying advice then, and there was no internet to research the issue either). Tearing may indeed provide an opportunity to stretch the frenulum as it heals. Whether this is no less desirable than formal surgery is a personal choice: its certainly cheaper, though perhaps slightly less dignified.