Sexual intercourse, or the marital embrace, is not just for the purpose of procreation, but also is to be a holy kind of bonding between husband and wife that is often misconstrued and believed to be merely earthly “fun” and while I suppose it should be fun and nothing is wrong with that, it should never be all about fun, as this objectifies the spouse–in essence making them into a play-thing. (I base such statements on “Theology of the Body” by St. John Paul II.)
As for foreplay, I have read that it is alright if it (intentionally) leads to sexual intercourse–fertility not being mentioned as it is not a requirement, although of course, artificial contraceptives may not be used–and that sexually pleasure is not deliberately allowed to peak during foreplay.