Is this considered cheating?

Other (comment)

So i found out that my boyfriend commented the drooling face emoji on some girl's picture. I don't know her but i know they went to school together. Anyways, i asked him if there was anything he'd like to tell me (not knowing i know about his comment) and he said he had nothing to say to me or own up to because "he hadn't done anything". We will have a conversation about it tomorrow, but i wanna give myself an idea of whether or not this is considered cheating, and if i should break it up with him for something this small