Interesting. But I would skip the marriage part. I see two ways it could go:
1) The more the buddy narrates the porn, the more the blind guy (and the buddy) get turned on. At one complicated maneuver in the porno, the blind guy doesn't quite follow the description, so he says, "show me." His buddy starts performing the act on him. Soon the two of them (previously straight as arrows) have discovered the joys of gay sex.
2) The "buddy" of the blind guy is really a platonic girlfriend. The rest goes the same as option 1, with them discovering that platonic friendship doesn't hold a candle to friendship with benefits.