I like the first idea, but it could be fleshed out a bit more. How about the two guys are friends/rivals at first. However the son is always just a little better or happens to luck out and win when it really matters. The other character could be full of resentment and in order to "win" he beds the sons mother and sends him pictures or video of the act. You could also add the second idea so that she is in a gang bang with the finale being with the one person he truly hates.