Dating a girl with boyfriend! Lost the chance?

Hello mates!

This is gonna be my first post here, though I often get myself reading a lot of topics here! I´m from Brazil, yet I don´t know if its a really important piece of information, mainly due to the fact that women are women despite the geographical localization =P.
Let´s get straight to the point, further introductions shall be made in the right section!

I´ve been chasing this girl from the gym for a long time, since I was dating another girl. Things started to get serious with the latter so I decided to stop chasing the first one, yet I still kept in touch with her. Unfortunately the relationship lasted only 3 months (and I spent the next 2 trying to recover - sometimes I still have setbacks).

A month and half ago I decided to try again with the gym girl. However she told me she had a boyfriend, and all that boyfriend talk women usually give and also, that she was to have a serious conversation with him - if you guys know what I mean - therefore, I backed up a little and gave her some time.

Two weeks ago she started giving me ioi´s at the gym again, so I realised that possibly she broke up with her boyfriend. I played a really tight game on her. I did everything right and with flair (it doesn´t happen so often!). Friday I "asked" (actually I didn´t give a choice hahaha) her out to a local and really nice bar.

Now comes the tough part. She told me (via sms) that she had 2 conditions before going out with me. First one that she couldn´t get too late at home, cause she was attending course next day. Second that I was aware of her situation with her boyfriend! This last f*ckn information really messed with me, although I pretended that I didn´t even read that - what, to my mind, turned her on.

So we went out. But I dind´t try ANYTHING with her! We spent the hole date just talking, I did some Kino, and so did she. It was obvious that she wanted me, but I couldn´t close-kiss her! Not that was beyond my abilities to do so, but even though I could change a lot of myself and believes I still can´t help women cheating their boyfriends! Something really blocks me - maybe it´s because I don´t want my next girlfriend doing this to me!

Next day I woke up feeling like s**t! Regreting every moment I could have spent making out with her but I didn´t! And now I have this feeling that I REALLY need to let this "don´t help to cheat" thing go! But I think I just lost my chance with her! She´s probably thinking that I´m fake, or that I´m gay, at least! Hahahah

Can you guys shed light on this problem? Should I try again? And mainly, HOW? Should I let it go??

I´m really looking forward for you inputs guys!!

Thanks in advance!

Oh man, this is tough. We're talking not so much about dating as we are ethics and personal convictions. If you want to make out with her, do it if she'll let you. If she's that type, she'll just make out with another guy anyway. You aren't really assisting her in cheating. If you prefer to back off because of her boyfriend, do so. Don't question what seems natural so much. Just go with it.