I think both you and ap are plan A sometimes and plan B at others. I don;t that that matters much.
I think the problem is I have made it clear that I want to be with her and so now she doesn't have to do any work to maintain that.
I think it's fine to let her know you want to be with her. The next step is to decide what you need from her for being together.
A member named Bigger says what I'm about to say better than I do, but I'l start.
You can say something like,
'I want to be with you, but only in a monogamous M.
If that sounds good to you, I need to to agree to being honest - no more lies. I need you to agree to IC with a goal of changing from betrayer to good partner. I need you to answer all my questions. I need you to take responsibility for your actions/behavior at all times. For example, you didn't make a mistake - you chose to conduct an A and to move out. You need to find a new job. You need to have no contact whatsoever with ap from now on.
If those are actions you will adopt, let's stay together. Otherwise, I'll help you pack.'
Of course, those are my main requirements, and you need to talk about your own, but feel free to use mine along with yours.
Society tells us both to get rid of cheaters and to forgive them, so you might as well choose what you want. You can hold your head high whether you D or R.
The thing is: you can D on your own, but R takes 2. IOW, you can want R, but it's not going to work unless your W does a lot of work. Right now, she's not doing it, so she's not a good candidate for R.
You need to figure out what you want from her and see if she'll deliver. If she agrees, R is possible. If she doesn't agree, R is not possible, no matter how much you want it.
If she does agree, you'll need to monitor her behavior and your responses to make sure she continues meeting your requirements - and you'll need to be willing to end R if she stops delivering.
Up to now, your requirements haven't been comprehensive enough - but I think it shows strength that you've come here because she's stopped delivering on even your simplest requirements.