the culling
by rantywoman
http://blog.socialjane.com/2014/01/Friendships-in-our-40s.html
I am not sure if this stems from the fact that when you turn 40 you gain a different sense of your own mortality or if people just become grumpier, but there is something about your 40s that makes it harder to sustain unfulfilling friendships. I have watched several of my other friends go through this and for each there came a point at which they became much more particular about whom they were willing to spend their available time with. For me, this has meant letting go of toxic people, frenemies, and people who were nice enough but just didn’t add much to my life. If you are used to having a large group of people you call friends, this culling of the herd can leave you feeling a little lost and lonely, even if it was your choice.
thebitterbabe 
I totally know where you are coming from. When you are in your twenties or early thirties, you put up with toxic “friends.” People who socialize with you, but also are also condescending or deceptive. Once you are 40 or so, it is exhausting putting up with disturbed or backstabbing types. Your instincts are more acute. This also applies to coworkers who should have a dangerous label on their foreheads!
I read an article once about how sometimes you have to retire friendships. I’ve done that too – and yep become a whole lot more choosy about who i invest my time in, now that I’m in my 40’s. (Oh god am I really that old….!)
Just this week I have not retired friendships, but cut them off at the knees, due to what I see as toxic, unhealthy, in fact downright mean behaviour. Its exhausting spending time with people who suck the life out of you, Im 46, I have plenty of life in me and I ain’t giving them a single breath any more.