Well, this is a very slippery slope. I know exactly how you feel when you say you're confused. I put my current boyfriend through the same thing. Him and I met when I already had a boyfriend but the boyfriend I had when I met him didn't treat me that well. He never showed me love or compassion and would ignore me for months at a time. He wouldn't even communicate with me enough to break it off - He was too chicken. I had secretly fallen in love with Mitchell (My current boyfriend) and he with me. But we both knew I had to break it off.
I went through stages where I thought my relationship could re-kindled and it confused Mitchell beyond belief. Mitchell felt like I was so special that he would wait all eternity. He waited almost a year for me until my ex and I finally broke-up. Mitchell and I have have now been dating for almost 2 years.
Now, that being said - it depends on the amount of dedication you have to this. My brother went through that same thing as well - with a girl at her work who had a boyfriend, my brother and the girl were "friends" My brother waited for a long time and finally realized that she will never leave him. I also have an older friend who is sleeping with a married man and is convinced he will eventually leave his family (but it will never happen).
I must honestly say that it's a very difficult subject to give advice on. Sometimes the wait is worth it - Sometimes it's a waste of time. It depends on how special the girl is and how much you care for her.
One thing I MUST tell you though is DO NOT underestimate yourself. You have to know you're worth finding other girls and that you can be loved by someone just as wonderful. I think my current boyfriend and I just got lucky because the changing of the tides just happened to sweep us down the same current. It's a lovely romance story but can be quite unrealistic. Then again, I won't tell you that you're not dedicated and in love because it's not my place and you could very well be madly in love.
My best advice is to us common sense because sometimes something as simple as simple logic is the best thing to use with such a complicated subject. One thing to remember is not to let only your heart do all the work - Healthy love requires the works of both your heart AND your brain. Love just tends to feel so magical you conclude that it must be only your heart's job, but just remind yourself that it also takes smarts; smarts enough to know when to hold on, and when to let go.
The best of luck to you!!! I'm rooting for ya!!!!
And thanks to surfinrach for your vote of faith in my opinion haha