I think LLs hate the idea of their HL partner getting fulfillment elsewhere because to an LL sex is more about power than anything. LLs feel most powerful when withholding sex has proven a guaranteed way to control the HL. The withholding of sex is like the metaphorical carrot on the stick, or it's like the string that allows the puppeteer to manipulate the marionette into utter submission.

But when the HL is worn down enough, probably a few years of systematic application of the LL methods, it's pretty much game over. The HL catches on that he/she will never be able to have a real bite of that carrot dangled on the stick, the marionette snaps the string and comes alive "Hey, I don't have to obey a power-hungry twisted mind anymore! Yipee!". It is a sudden and possibly irreversible change. Systematic withholding of sex in a LTR exerts such enormous pressure on the HL that they will eventually break one way or another.

So the LL goes in his/her mind something like "Oh shit! Better untie that carrot from the stick and offer a tiny little bite, here, mmmm, want some carrot? What? Here, it's shredded now, with sugar! What do you mean you don't want it?! Here, it's gourmet Gâteau aux Carottes now, with whipped cream and cherry on top. I'll throw in the kitchen sink as an extra bonus cause I luuuuuuuuuuuuuuuuv you, god dammit, so you better start obeying me again! Please have the carrot, please?" - goes the LL mind in chaotic panic.

Whenever someone is manipulating you in any way, using your own motivations in an attempt to twist your actions towards serving their own private agendas... you just have to take that weapon pointed at you, metaphorically, wrangle it out of their hands and disarm them. "You know, I've been thinking about this carrot... It's just too much bullshit, it's always jumping through hoops and patience and space and understanding etc. etc. etc. yeah, no, I'm fine, no carrot right now, thanks." - goes the HL.

And that is the moment when the ball goes into the LL court. What can and what will the LL do to go back from being revealed as a puppeteer. It's a case of broken trust and that's no ordinary thing to fix. Sometimes this kind of damage can be permanent. If the HL starts to question the validity, the very essence of the relationship, just bringing the carrot back to the table is no longer good enough. It's a bigger problem now - an issue of love and respect, trust and the abuse of it, and so on. The LL had a chance to fix a minor carrot issue in a timely manner, but they chose to allow a carrot issue to grow to catastrophic proportions.