Questions

A guy I've gotten to know and I often engage in a lot of banter.
We have the same sense of humor, so we often call one another ugly names and then laugh our asses off.
He calls me Quasimodo, I call him Dickhead. It's something we thoroughly enjoy.
We don't hang out outside of our mutual community, but we do often spend time together when we're there.
Recently I joked about his behaviour to which he replied "but you still love me" then waited for my reply. I pinched my fingers together a eventually said "just a tiny bit, but only if it's mutual," he replied by pinching his fingers like I did and said "just a tiny bit". Give two playful punches in my belly and walked away.
I jokingly exclaimed "Hey, my baby!" To which he replied "Doesn't it sit on your backside?" Referring to my ass. I laughed along and said it was a conjoined twin, and the two of us kept joking about my "twins" for a minute before I left.
We have interactions like this more often than not, which is why I thought he might be interested. However, I just now learned he is in a relationship with someone.
Is this kind of behaviour normal when you're in a relationship or would you consider it (emotional) cheating or whatever term you'd use?