I really feel for you, but there is one thing i have learnt. I cant say it will definitely apply in your circumstances, but these things generally have the same conclusion.
Affairs - as this is what it essentially is, rarely come to anything satisfactory for the partner who isnt attached.
I have been in your situation for almost 5 years (but with a man). He is married but has no 'marriage'. It means buggerall. They will almost always stay with their permanent partner. If they were that unhappy and wanted you, they would leave. I know it hurts but that is unfortunately the reality. All the excuses under the sun are just that. Excuses.
I cant really advise you as im living the same life. But if i was too, i would say dont waste any more of your life. You could still be where you are this time next year or in ten years. And the more time you stay, you justify even more time staying by saying you have stayed this long.... !
I really feel for you x