mchael,
I've been through that situation too.
For me, it got frustrating bc she would call me when he was gone, when they were fighting, or when she had spare time: but never otherwise.
She expected me to jump at the chance to see her when she was available, but had no problem blowing me off. She pretty much expected me to arrange my schedule to fit her in, but would not do the same for me.
It got to the point where she had no idea what was going on in my life: it was all about her. It was a one-sided friendship.
One night I sat her down and talked about it. I told her that I loved her, and I wanted to spend time with her and be friends, but I was not ok with being used. I reminded her of all the great times we'd had, and how I wanted to be part of her life. I gave her the exact things I required of her in order to keep being there for her: basic respect of my time, calling to see how I am every once in a while, not constantly blowing me off, etc.
I asked if she could do that at this point in her life.
She said she didn't know. Our friendship changed after that. I stopped spending time with her bc she wasn't able to be there for me.
It's true that sometimes priorities change and friends can drift apart.
She might be a bit obsessive or have unhealthy patterns, but it's not your job to fix them. That's up to her.
You just gotta decide how much of yourself you can give to the relationship, if any at all, without getting hurt.
Only you know
good luck n' love