While I think it's reasonable to keep an eye out to a point, make sure you're not crossing the line where you break trust with an innocent partner and risk the relationship.
Back when my marriage was monogamous, if this had happened and my spouse had asked me about it, fair play. But if he then started keeping tabs on my whereabouts, accessed my phone, stepped over the line in any way to break my trust by acting controlling or violating my privacy, just based on a random anonymous message, I'm not sure I'd have been ok staying with him.
Update?? It has been 48 hours
While I think it's reasonable to keep an eye out to a point, make sure you're not crossing the line where you break trust with an innocent partner and risk the relationship.
Back when my marriage was monogamous, if this had happened and my spouse had asked me about it, fair play. But if he then started keeping tabs on my whereabouts, accessed my phone, stepped over the line in any way to break my trust by acting controlling or violating my privacy, just based on a random anonymous message, I'm not sure I'd have been ok staying with him.
I'm a manager. Never touch anyone. No non professional text messages. No non professional emails.
Your dude is a creep.
Don't do it. I mean, I get it, I have felt like that many times, but you're only hurting them, not helping.