So what do you think you have done that has contributed to your M getting to this point? Those are the things you should be working on while you give her space.
With regards to your M, a lot of what you're doing reminds me of my own sitch. You play nice, you hang out when you can, you make plans, and things seem good to you. Then she breaks plans, or stays out late, or whatever, and you are stressed out and arguing with her, at which point she talks D. That my friend is a roller coaster ride I bought many tickets for....and it $ucks.
So how do you get off the ride? One, you work on yourself as I mentioned above. Two, you GAL....hard. You meet new people, you work out, you get busy, you start enjoying life outside of your M. Three, you stop being available for your W and stop accepting all her invitations to do things. And four, you learn to break your codependent behavior and respect yourself.
Believe me, the longer you stay on this ride, the worse shape you will be in as well as your M. It doesn't get better until, as Acc said, you do something different.
