Becca and kdt26417 give other examples of how to employ having "limits" via other methods:
- doing nothing "life permanent" at this time
- giving a year's run before the next check in point.
I didn't think of those at first but on reflection -- I've had both methods at other times. Just right now, "3 strikes" serves me best. I think that's helpful to remember -- what serves you best at one time of your life may not be the thing at another time in your life. Having various tools in the "coping toolbox" helps. Being willing to be flexible can help in life's journey too.
Having limits and boundaries are part of what help create the personal standard in the healthy relationships you want to keep for yourself. What you will and will NOT tolerate. What does and does NOT feed you so you can thrive.
Could try some of the examples ones already given to see if they will serve you, could mix-and-match approaches, or create something totally brand new as a personal limit and come back to share that info with others.
By knowing yourself and the standard you create for yourself, that can help you assess the relationship you are in. Does it meets the bar or not? Can I be healthy here or not?
Hope things are going ok over there.