[Daniel.]

No girl can 'stay the way she is'

I think your only option if you MUST keep those preferences in that order is that you organize her to spend time with you while you study. Though you say that you do courses and all that which means she wouldn't be able to participate. Females aren't very patient when it comes to wanting attention from a guy (honestly girls I don't mean that offensively). You need to show this girl what is more important. Your schooling or her.
If It's not going to work out then let her fall and then get a girlfriend or go back to her after your schooling is finished. In my life schooling was always the last thing on my mind, I'm not an idiot however I did really well at school apart from all the bullying, which is why females were always my first preference, everything else was second best. Which is why I did so much better then anyone else with the ladies. I wagged school to be with them, showered them in love, went out of my way to be romantic etc etc.

You need to rearrange your preferences. Those courses sound bad. I'm joining the army and I'm going to have almost no time to do anything so when I come back is when I'm going to have all the fun I can.

I cant expect my girlfriend to stay with me when I'm gone for 8 months.

Lastly these promise rings. Don't your dare think that once you both have them shes not inclined to change her mind because you suddenly have a green light to study study study meaning the promise ring is a "No I will not break up with you because you show me no attention". Promise ring or not, shes on the border of losing interest in you.

I think I should say one more thing. I have no idea what your religion entails so I don't know about what I'm about to say. Maybe you should get her alone and give her a few orgasms or just spoil the fuck out of her sexually, if your any good she'll love it and she'll know how much you love her. This can buy you some time to go study and all that. Even if you suck it'll still be a bonding experience.

~ImI