It was cruel and selfish of Snape to do this to Harry when obviously Harry cares for Snape and Snape for Harry. I would've preferred Harry had found out and given hell to Snape for what he did, because Snape certainly doesn't deserve Harry's devotion if he nonchalantly starts the dalliance with the shop-keeper and has no regrets about it. And I especially don't believe Snape's comment of "I have all I need" because if he did, he wouldn't have started the affair no matter how brief. I don't like infidelity stories.