I am a little late to the party, but I will just add the “statutory” answer (I am a lawyer after all).
This question comes up all the time, but, it’s not really that complicated (if you are allowed to talk bluntly, which I will).
To sum it up, there are really only three hard and fast rules:
- The man and woman must have the intention of the man climaxing inside the woman;
- The woman’s climax should come “within the context of” intercourse, where the man and the woman have the intention of the man climaxing inside the woman; and
- No artificial contraceptives may be used with the intention of preventing pregnancy.
These are the clear limitations laid out by the magisterium. Other Catholics have other opinions out there about other restrictions and things that are “immoral”, and people are of course free to have (and live by) those opinions. However, they are just opinions and not binding on all Catholics. Those are the only three defined hard and fast rules about sexual activity between married couples. If both couples are fine with an activity, and it doesn’t violate one of those three rules, it’s perfectly permissible and between the married couple.
With regard to 1, there is the qualifier “the intention of” because, especially when you are newly married, there might be some “oops” moments. If you are truly waiting for marriage, as a man, you might be too excited and, while you and your wife intend for you to finish inside the woman, you may be overstimulated and you may climax before you get to that point. If that happens, don’t worry about it and obsessed that you “sinned” or weren’t “open to life.” Your wife will likely feel desirable and everything is fine. Speaking from experience, for Catholic couples that wait until marriage, that type of thing can happen, especially as newlyweds.
With regard to 2, essentially that means no sexual activity outside of “the context of intercourse.” No mutual masturbation. Now, there is no strict rule on “how long,” but, in the couples judgment, it must be within the context of intercourse. If the man climaxes inside the woman, they talk lay in bed and talk and cuddle for 5 minutes, and then the man helps the woman finish, probably fine. If the man finishes inside the woman; he heads out the door to pick up some groceries and wash his car, 2 hours later comes back to finish off his wife, probably not “within the context” of the original act. But, what that means is within the prudent discretion of the couple.
The qualifier is also added “within the intention of…” because, there may be times when, in the course of sexual activity, the man helps the woman achieve climax, with the intention of later climaxing inside the woman (also fine). However, before the man can climax, 3 year old daughter knocks on the door crying with a tummy Ache, the smoke detector goes off, etc., and the man doesn’t climax. Don’t obsess about it, it wasn’t a sin. The intention was right.
The point is that sex should be unitive and procreative. This means that for sexual activity within a married, the three concrete rules are that the man and the woman must intend that:
(1) the man climaxes inside the woman; and
(2) The woman’s climax occurs “within the context of” (whether before, after or during) intercourse.
(3) Not to use artificial contraception with the intention of preventing pregnancy.
Don’t sweat it. If you follow those three rules, then nothing you are doing is violating what the magisterium teaches. There are endless discussions about various people’s opinions about what is or isn’t compatible with the “procreative” or “unitive” aspects of sex. Those are all interesting, but they are just opinions.
Of course, the other “subjective” rule is that everything done should be respectful and loving to the other spouse. So, even if it’s not “morally impermissible” to, for example, use handcuffs. If one spouse finds it disrespectful, unloving, or demeanining, then it should not be done.
