Is it a red flag that my girlfriend with whom I had a rough patch lately texts with a guy?

She met this guy a few days ago and they've started texting each other and she eats with him although he has a girlfriend. We are going through a bad time in our relationship and she tells me they are just friendly and platonic. However, isn't it strange that she got that close to the guy although she barely has female friends and friends in general? She keeps telling me she gets on better with guys.

Is it a red flag that my girlfriend with whom I had a rough patch lately texts with a guy?
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