Is my guy friend cheating?

I had a guy friend who hides the fact that he has a partner from me but told our common friend. When I confronted the guy he said it was not important to disclose it but in the meantime, we kept becoming emotionally intimate and sharing everything to each other, praising each other, giving each other attention often, motivating each other and turning to each other when the going gets tough.

He also complains to me of the bad habits of his girlfriend. Now, he decided to finally come back to our city and leave his girlfriend's city because he said he feels safer here.

He mentioned to me in the past that I'm the only one who understands him and he thanked me for being there for him. Is this emotional cheating? He did hide and went outside last time when he was still in the other city whenever we talk.

Also, it looks like the girlfriend doesn't know i exist but in one of their fights, he told me he boasted to the girlfriend that someone from his city can help him, and the girlfriend didn't believe.

Is my guy friend cheating?
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