Here is what we do know:
You may not spill the seed, and that means no contraception and to finish vaginally. You may not commit adultery, meaning that sex is for marriage, and that being a man and a women, by the way.
Did I leave anything out?
There is not that much else on the subject that rises to the level of authentic magisterial teaching on this. People will have to accept the fact that they need to figure this out for themselves, and try their best to keep their moral compass despite emotions, passions (these can be VERY powerful), and other factors, and simply to try their best to be loving and giving. … and in the end you have to figure out how you can please one another, and whether you have any room for fliexibility, and if you do, what is the cost of it, and is it worth it.