What is wrong with a newlywed who is engaging in sexual banter with an ex?

What is wrong with a guy married 4 months who is texting and engaging in sexual banter with an ex? And reminiscing about their past sex life? He says he is very happily married, loves married life, and truly values his wife...However his sexy, racy texting is not consistent with what he says about being so happy as a newlywed....