I understand, and you're getting advice right now from a late twenty-something. And I know what its like to date while having mental illness- the scarcity mindset sets in and you tell yourself you would never get a chance like this again. Ultimately, you project this and it makes it easier for her to have her cake and eat it, too. I still stand by my word, there may be someone better than her for you and ultimately it's your dignity that counts, because if this progresses and goes nowhere you'll suffer a blow. In my opinion it's just not wise to count on a girl who has a boyfriend but is having a relationship behind his back. No matter how dried up things have been and for how long, it's still a respect and dignity issue. If I were in your shoes, I wouldn't pursue it any further. Forget the drama that can result, just the act of waiting on a woman who knows your weakness and why you haven't moved on and takes advantage of that is enough to demoralize me. Then again, I'm younger. Plus, I have a certain personality that allows me to make black and white decisions (call it a curse or whatever, it's created as well as solved problems for me).