What does it mean when a guy says it’s not like that about another woman?

So I found out that my boyfriend of 10 years has been texting a coworker behind my back for 5 years, and there was sexual sly references in the messages, when I confronted him about it he said “It’s not like that” I want to know what your opinion is?

What does it mean when a guy says it’s not like that about another woman?
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