Isolating

I have the most amazing group of friends. We've been together since our first year of high school and even with everyone now going to college, working and living in different cities, we still managed to see each other all the time.
I don't even have the words to describe the love we have for each other.
When we go out, I'm definitely one of the most fun people to be around. I drink, I joke and have a blast. But at the same time, I always feel like I'm about to have a breakdown. Sometimes I have to go the bathroom just so I can breath and get myself together. 
For the past year though, I've been isolating myself more and more. 
It has been getting really hard to keep up with the pretending.
And now my friends have gone from texting "I miss you" and "I wanna see you" to nothing at all. They probably think I'm ignoring them and I feel like they're slowly giving up on me and on our friendship because of it. And I don't blame them.
I just feel tired and don't have the strength to do anything.
I miss being able to keep up with the pretending. I miss seeing my friends everyday.