Hm... I interacted with a girl much like your gf (wasn't actually a girlfriend, but anyway)... now from what you say about her, it seems that she might not love you at all, but just your attention. There are some people like that - they just need the self-esteem boost that comes from having someone that cares a lot about them... and then when they get in a relationship they don't want to let go of it by ANY means - even if they don't really like the person anymore. It was like that with the girl I met - when I asked her to be my gf she didn't say yes or no because she didn't want me but she didn't want me to walk away either, and it went on for months...
So you don't really suck, but I think step 1 is to break it off for good, respectfully but clearly. Which means no contact, and ignoring all her attempts at getting attention. That's what I did anyway, and believe me she was a pain for a while, but she got the message quickly.
After that, by all means go take your shot at the other one, regardless of the odds - life's too short. Hope I helped (but take my words with a big grain of salt)
(um português por aqui? xD)
Time to stop complaining when there is no reason to. Life's good, man.