Have you given yourself a time frame? I find that helps. Tell yourself "I'll give this six months, or 9 months, or a year of my VERY BEST effort, and then I must move on to protect my own heart."
Do NOT communicate this deadline with HER< but it does help if you have one for yourself.
Another thing that I found helpful was that when I was feeling like a complete SAP, I would remind myself THAT I HAD A PLAN. That she may THINK she is duping me this day, but my patience was part of MY plan, to DB, GAL and show my kids that you don't just cut and run when things get tough.
And PRAY. ASK for patience, and for a steadfast heart.
