wife hardends heart-2

[planet]

What to do do with the 'not quite OM'?
He's always around. He comes by the house almost every weekend and stayed for the for long hours returning only late at night. He also will come over for dinner if he happens to be around on some weekdays. Sometimes I'm present and sometimes I'm not.
I'm not cool with all this. Clearly W is smitten but I doubt she had crossed the line.
They sit pretty close to each other which makes me very uncomfortable. The fact that W will ask him to do stuffs around the house makes me very uncomfortable. Fact that she tells him a lot of things and he seems to acknowledge them makes me uncomfortable. Fact that he tries to be like a 'father' to my kids makes me angry. Feels like being replaced right in front of me.
What does she wants from me? She'll ask me if I would like to join if they have already made plans to go out all the time. The not quite OM will invite W out over the phone and she will in turn ask me if I would like to join. I have been GAL over the weekends but they wait until I'm back before going out for dinner. But that is before I have requested W to inform me whenever she wants to take the kids out. Previously she have taken the kids out for lunch with the 'not quite OM' without informing me. maybe a few more outings too.
There is something going on but I cannot say I'm 100%. Other people have been noticing too. It's pretty confusing.
What do I do? Do I confront? My situation is not improving with him in the picture. It's like I'm not needed even as a father to my kids.