The man that Scarlett was kissing, is Brandon Robert Young, Clare Bowen’s real life husband.
Apparently he (the character) was in in the band with Deacon, and I guess that’s how they met.
Kind of odd, but they were out of time to wrap up storylines. It wouldn’t have been believable, if, after all this time, and all their back and forth, suddenly Scarlett and Gunnar had been back together.