She ends it. Not a blowup, just that the relationship ran out of momentum. Three weeks later she's with someone new. You wonder what you missed, what you could have done differently. Probably you tried harder near the end: more attentive, more present, making it clear you were invested.
That's the part worth examining.
The game
The pipeline is an exit strategy. Rather than leave a relationship and face the open market — cold matches, slow conversations, starting over — she keeps a prospect warm in the background. When the prospect is ready, she exits to it. No gap.
What makes this work is your behavior. She needs you to stay put long enough for the prospect to develop. Your reliability is what gives her the time she needs. The more committed you are, the more comfortable her timeline.
From inside the relationship you can't see this directly. What you see is distance — she's less present, a little vague. The natural response is to close that distance: more investment, more effort, demonstrate that you're worth keeping. Which is exactly the wrong move. You're stabilizing a situation that was already being wound down.
Dominated strategies
Being reliably committed to someone who might be hedging. You can't know for certain which situation you're in — real distance versus exit sequence. But the asymmetry matters: if she's not running a pipeline, a little uncertainty from you costs almost nothing. If she is, your certainty is what enables her to take her time.
Responding to distance with more investment is dominated because it makes your position worse in both cases. If things were salvageable, stability wasn't the missing piece. If they weren't, you funded her transition.