<human>: Summarize the given text in a few sentences.

To give some background, me and my wife have been married for 15 years now, with kids as well. We've always done well together...occasional arguments, but nothing too serious and we both manage to balance our professional and family lives well.

Now, my wife is friends with this guy in work. He joined a couple of years ago, and I only heard about him in the passing. About four or five months ago though, his name started to come up more often, and him and my wife started going to the gym together.

Again, that didn't bother me. She goes to the gym. So does he. Makes sense to go together sometimes I guess. I run occasionally, but not enough to warrant paying a gym membership so again, no problem with that.

I did become worried as I heard some more about him. Turns out this guy has been making his way around the office a bit, and has slept with a couple of my wife's friends. But, again, said friends were either divorced or single, so while it bugs me a little bit, it's not a major problem.

What is worrying me though is just how friendly they seem to be. She always says things like, "He's such an asshole.", but will follow it up with something nice with a smile, or something along those lines. She'll jokingly call him handsome when in company, which was fine as a joke at first, but is starting to annoy me.

The other week he was over for dinner. I noticed how close him and my wife seemed to be. They had all their own little in jokes, and she'd sit next to him on the couch, really close to him.

It' starting to really get to me. My wife is quite attractive, and she's spending so much time (often alone) with this younger, confident and fairly athletic guy who some of her friends have already slept with.

Any ideas what I should do?
<bot>: married to wife in good relationship, wife starts hanging out with younger work colleague a lot and goes to gym with him, worried they're getting too close and flirtatious