Why do we say that we're having sex "with" someone, but making love "to" someone? The phrase "having sex" suggests a much shallower emotional bond than "making love," but the preposition "with" seems much more consensual and less one-directional than "to."
Saying you're making love "to" someone implies that they're the direct object, and you're just doin' em. Not the image you want to conjure up if you're going for the whole "making love" thing.
I think that we should switch these two prepositions so they're used with the other phrase.