I think when a husband starts getting more comfort from seeing his colleague’s notifications than from his wife, then understand that a virus has entered the system. It doesn’t have to be physical; just a mental wander is enough.
The new “spark” that a husband is getting at this age is actually a cheap way to escape the office boredom. He is becoming cool with his colleague because there are no responsibilities or home problems, and this is the biggest red flag. If he is ignoring you and is glued to his phone, then he is not being friendly but is trying to fill the emptiness of his married life from outside.
Is this chatting? Maybe not “full blown” yet, but definitely “micro chatting”. If a husband is feeling flirtatious outside after 4 years of marriage, then it means that he is not respecting the boundaries of the marriage. you are being “uncomfortable” is enough proof that something is wrong.