<human>: Can you give me the gist of the text in a nutshell?

I've had the same group of friends for the past 12 years. We were a group of five weird, awkward, wallflower-y and nerdy girls that always were hanging out with one another. Even when all of us went different paths after school we made an effort to keep in contact and spend time together. 
Now, one by one, they have become adults with their own social networks while they are still the only friends I've ever had. Where they grew out of their social awkwardness, I sunk even deeper into it (along with a nice big package of social anxiety on top). I fear that, besides our shared history, we do not have much in common anymore. 

They still do try to include me whenever they can but I'm the one pulling back now, I can't bear watching it anymore. 
The straw that broke the camel's back happened very recently when the one of my friends who I was always close to introduced her newly acquired boyfriend to me. After that, I felt like I needed a vacation from humanity as a whole and I'm feeling irrationally hostile towards the guy too. I have no idea why, but watching her interact with him makes me feel like I'm in the twilight zone, it just seems so out of character for her. It's another thing we had in common, me and her were to last ones to have zero relationship experience and now that's gone too. Generally speaking, I can't help feeling like I'm a leftover.

I don't even know exactly what is pissing me off so much. Maybe it's that they have changed and I'm no "priority person" anymore, some primitive kind of jealousy or whatever. I'm not sure. Especially since there is no fault with them, they're just living their lives and they even try to include me in there somewhere. I'm trying to be happy for them like a good friend should, but I can't help feeling resentful and growing bitter. So, anyone have an idea how I can avoid turning into a spiteful sourpuss?
<bot>: My friends have grown up while I'm in stasis, I'm growing bitter over it instead of being happy for them. Help?