When he starts visualizing the sexual fantasies of anyone he touches, a love-struck freshman has one week to find true love or be doomed to rule hell. Title: SixSixSix

I'm always for simplification, however, in this instance, I still fail to see the cause and effect connecting the inciting incident and goal. Him getting these powers out of the blue doesn't logically connect with him needing to find true love. What does true love mean? Must he be married? Engaged? Committed? Love is subjective and even in the fairy tails requires a symbolic act of some sort, what's his?

Lastly, what's at stake? So what if he visualizes other people's desires, is that a bad thing? What does he have to lose that forces him to make a deal with the devil?

Little Nicky kind of did this already. In that they answered pretty much all the questions raised in this thread. The Devil is dying and his son (born to an angel after a drunken night with the Devil) must venture off into the human world to find a cure for his father.? It's not the same plot, but explores similar father/son themes between the devil and his offspring.

After reading your explanations, I think the plot is the problem - normally the case when a logline struggles to work. Being the Devil he can damn well do what ever he wants, deal or no deal, so binding him to a promise doesn't make much sense.
Is there something the son must do or else? Like in Little Nicky that the devil can't deny or renege on?? Is there a more compelling set of circumstances for both son and father?

If this story has not been written yet, there could be a different take on it which might help.
The idea would be this:
A popular high school Quarterback who thinks he's Gods gift to women makes a bet with the Devil, that he can seduce the school Virgin who has dedicated herself to purity.
Now he has one week. If he succeeds he will be granted his wish, to be the star QB at Ohio State. If he fails he will be sent directly to Hell, no passing go, no get out of jail card.

The devil, in the mean time, will play tricks on him to make his mission even harder.