It’s often said, and in my experience seems to be true, that when you reunite with them it gets shorter each time before the nightmare begins. Why is this?
Because when a relationship with a borderline ends, regardless of who ended it and what went down, the borderline interprets that as abandonment, the worst thing that can happen, and if you get back together, there's less trust, more fear. So my experience, echoed many times here, is the idealization phase is shorter, as is the relationship, with each recycle.