I agree with the no contact. I am/was/is in a similar situation, except we have had sex once, but she keeps me on the back burner, and like the OP hides or lies current relationships but wants me to mop up when they end. She goes dark or gets snippy every time she is in a relationship, so it's not too hard to tell. I've sort of allowed myself to be in the on deck circle for years, mainly because I don't have to put much in to keep the back burner status. Add to that, she's an HB8 and 31 - I am 50, plus a freak in the sheets so I do tend to put up with a little more to stay in her orbit.
Lately, and being inspired to continue it by these forums, I have had her in NC for 44 days today. That's a personal best. Usually they go no longer than 2-3 weeks before she chirps back in but this time she has an ex-convict boyfriend (who she denies is her boyfriend because "I hate labels") who spends at least 3 nights a week with her. So she has done the normal liking of my occasional social media post, just to sort of kick test me to make sure I'm still in her orbit. I'm like her Personal Floatation device.
I do want to see if I can make the full 60 day NC. Also, full disclosure - she is a side piece and I am married. I've been way too beta with this one, in hindsight, which is why she keeps waving in these alpha, bad-boy, white trash dogs. She's a single mom whose mother is raising her kid mostly so the guys don't have to deal with the normal single mom BS. That's why they stay longer than most but even the trash moves on eventually - or mostly she nexts them because she is super shady and always has a flock of Tinder weenies orbiting her.