Much like what happened in Ted and Emmett's situation, Daphne and Justin sleeping together proved to be risky, and it could have really cost them their friendship. Even if it's for one night and not a relationship, I think whenever people are friends and they decide to cross that boundary, you'll always run the risk of destroying it. Justin had already made himself clear beforehand that some weirdness could happen, and it did. But I think it's only natural that Daphne caught feelings for him because that's such an emotional thing to be intimate with someone for the first time, just as it was for Justin. So if anyone should know what it's like to experience such a thing, it would be him.
