I've learned in my nearly 40 years that all friendships, acquaintances, girlfriends, wives, whatever are all based on a period of time & once that period ends due to social status changes, marriages, divorces, whatever, it is over.

It fucking sucks.

Seriously: just stop trying to make one-on-one, time-sensitive plans with Mary. Invite her along for parties, or when you and a few others are going for drinks and will be at the bar for a while. She's clearly fun to be around, just unreliable. And she clearly doesn't need you to be her lap dog. Push her into your periphery and she will almost certainly not even notice--she's got a gaggle of friends, hasn't she?

Don't break a friendship entirely over something as forgivable as flakiness. It's a tolerable, even endearing trait as long as you don't put yourself in situations where you need to rely on the person.

To the LW, I sympathize, because I've been through a very similar situation with a former best friend. In my case I moved back to our city after about 3 years away (time during with my former friend was very supportive and helpful; I too stayed with her when moving back, etc.) and found that the girl I'd really loved suddenly had no time for me. She could never be bothered to make a plan, when we did make one, she'd cancel with no excuse, or show up late and leave early for "other parties" etc. When we did hang out, she seemed both bored and guarded. I found it incredibly hurtful and confronted her, but she denied that things were as I perceived or that she treated me any differently/worse than she treated anyone else. Which, I knew wasn't true because we have many mutual friends who she will make plans with, etc.

I found her treatment too hurtful to continue the friendship, which I guess goes with Cary's advice to look at the reality of the present and let the past go. But. It's been very painful to me for two years now. I still dwell on it, and regret being out of touch with her, and wish I could understand WHY and what happened.

Like you, I am in a relationship and my friend is single. It has been theorized by our mutual friends that deep down she's really jealous of my happy married life and thus can't cope with spending time with me. I still can't see that as emotionally resonant considering the situation, but maybe....?

The other theory I've heard is that women in their 30s are going through a lot of huge life changes and they get very competitive and weird with each other and lots of longtime friendships bust up, especially when there are differences in marriage/kids/stay-at-home v. working, etc.

It's sad. I wish it weren't this way. I'd love to hear the perspective of the single, 30s friend-dumpees out there, and maybe from women older who have been through this period and see it more clearly in hindsight.

The 30s is a difficult decade for men and women. The 20s are fun and exciting and the 40s, 50s, 60s and beyond are for coming into our own.

This may sound hokey, but most people don't really know who they are in their 30s in the U.S. So many people do what they "should" do. This includes getting married, having kids, buying an SUV that you really never wanted or moving to some dead suburb. If you're single, you're 'dating' like mad - either online or out 'partying' like your friend - because you're trying to meet "the one."

The 30s are the best decade for moving ahead in your career and the absolute worst on a personal level. Of course this is just my opinion - but they're letting me write in this box....

You are losing your friendship, but not the friend, as one reader pointed out. You will know her on a superficial level. It is a terrible loss, but it is as normal as the leaves changing in fall (if you live on the East or in the midwest).

Both of you will grow and change over the next several years. Maybe she'll get tired of her lifestyle and change again in her 40s. You too will change.

It's bittersweet to say goodbye, but life is all about change. Nothing stays the same. Look at the watch on your wrist for 60 seconds. The hand will move. It's all in flux. What you are experiencing is just part of the deal. These losses will happen again, but you will grow for having experienced them. And you will like who you become.

I went through a similar time with a friend on mine during university... we pretty much stopped hanging out since frankly we were in pretty different places.

Mary sounds like right now she wants to be the center of attention, and do a lot of activities that the LW has no interest in. See it from her point of view as well though -- the friend she used to do a lot of stuff with is now in a committed relationship, and isn't into going out and "picking up" as she used to be. That's a loss for Mary. She sounds like she's gone further down a path that the LW decided to fork off from.

I'm not excusing her behaviour, just saying that as she has changed from the "college days" so has the LW.

The thing is, sometimes as time passes our paths come back together. Maybe Mary will get married and settle down. Maybe she'll have kids around the same age as the LW, and no longer want to hang with 35 people and spend lots of money on stuff. Or maybe the LW will break up with her partner, and decide that she's bored and sick of the hiking and musem-going life, and ready to join Mary back at the party.

You can let a friendship slide a bit without abandoning it all together. Things might change, or maybe they won't. Time will tell.