Oh my gosh, that is devastating. Have you sat down with him and talked to him? As difficult and as heart breaking as it is, maybe there happened to be something came up or a reason why it happened.
I would surely hope that as much as you might not be close for a while because of this, it wouldn't affect your relationship. Life is going to be bringing up some trials, some big life trials that go past the trading of a cow for a horse-if it does affect your relationship, you have bigger problems on your hands than a horse.