I like Saint Valentine. I am also a big fan of Christian marriage, and he was martyred for illegally presiding over Christian marriages. Through some bizarre accident of history, his feast-day is observed by the secular world, but the Church has taken him off the General Calendar. Unfortunately, I think very few people who mark this day on their personal calendars ever consider the life of the saint or the reason he died. This is but a reflection of a deeper problem: just as the world celebrates the feast of the patron of love without actually celebrating the patron himself, so also the world celebrates romantic love without actually thinking much about what love is in the first place.
In his book Love and Responsibility (written before he became Pope), Saint John Paul II impugns the idea that the point of a relationship is for both members to derive pleasure from it. The problem with this idea is that pleasure is not really a goal; there is no pleasure except pleasure in something. We eat cake for pleasure. We do not eat pleasure directly. No cake, no pleasure. Somehow, the world is trying to eat for pleasure without thinking too much about the step where you actually put food in the mouth. Such is a relationship of pure pleasure.
Any relationship, not just marriage, needs to be based on a common goal. For example, hunting buddies have a relationship based on hunting. These sorts of relationships often lead to pleasure, but a relationship that is only founded upon mutual pleasure is actually the most unstable, because pleasure is so ephemeral. This can be said of emotional as well as physical pleasures. The deep feeling of contentment that arises when silently beholding a sunset with a lover is certainly a high pleasure, even the stuff of poetry, but that delight must give way to a chilly night. When night falls, something more than the sunset must remain to keep the relationship together.