Confronted my boyfriend yesterday about him texting another girl, he said "he is not hiding anything". Do you think he is lying?

My boyfriend is texting with his female coworker whenever I'm not around.

I've had enough so I confronted him with the words "why aren't you texting/calling her whenever I'm not around, are you hiding sth?".

He was visibly confused and said "I'm not hiding anything".

Confronted my boyfriend yesterday about him texting another girl, he said "he is not hiding anything". Do you think he is lying?
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