You wrote this so well; I can almost FEEL what you are feeling. It sounds very strong.
I do not believe you are selfish; I would banish the negative-self talk!
My opinion: I don't think you can force anyone to love you back. I don't think you can "fight" for anyone to love you back.
If you want him to continue to make good choices in his life, I think you need to continue allowing him to make good choices. He knows where you live. He once loved you (I assume?!). He has a girlfriend right now. I think you continue going on with your life, dating, being the person you want to be. If he is still interested in you, he will make choices that allows him to spend more time with you, while also telling his current girlfriend that he'd like to "start seeing other people". I would not enable him to make any bad choices in his life (ie, cheating on his current girlfriend). You've already been down the "bad decision" road with him, and I assume/hope you do not want to be the culprit of another bad decision ("bad decision" would be, again, not being faithful or lying to either you or his current girlfriend...or even himself).
Love is fair, love is kind. Love is patient. Allow him love in his life, whether it be with your or his current girlfriend.
Have you looked at why you are so passionate about this guy? This is a HUGE leap, so please forgive me, but have you had any experiences in your life similar to this...where you want what you can't have, and once you have it, you are not as passionate about it anymore?
Another thought: perhaps you two are "meant" to be together, but now is not the right moment. You are free to let him know how you feel (once!), tell him you respect his current relationship and want him to make good choices for himself...whether that be with you in the picture or not. Do not go overboard and "fight for him"...that is a lose-lose-lose situation for all three of you. Let him know how you feel. If he feels the same way now, later, or never...allow him space to make good decisions for himself. In the meantime, continue developing yourself to be the woman he (or any other partner) would want to be around...but most importantly, be the person YOU want to be around! Don't intrude on his life, if he says he's "not sure" about his feelings for you, or if is currently happy. Allow him space to feel his feelings and live his life. That's truly loving the person, in my opinion!