Does she not want to be friends anymore?

So me and my bestfriend have been friends for coming up five years, but we've only been bestfriends for coming up 3 years.
We were so close. We did everything together.
But last year this other girl came along and she started ditching me to hang out for her cause I know this other girl doesn't really like me.

We also use to joke around and say we were married on facebook, but know she's doing this with this other girl.

We just haven't been the same since this girl became her friend. She's my bestfriend and she's one of the only reasons I'm still alive.
And I know I'm sorta boring because during the summer I fall back into a deep depression and I can barley make it out of the sadness. And that means I'm not really up for hanging out like she wants to.

I just don't know what to do. Please help! Cx