I'm going to walk home from my girlfriends apartment
Why would you walk home from her place? It's pretty far.
I can't afford to take a taxi at that distance. No choice but walking.
That's up to you, if you wanna walk that far. Though why can't your girlfriend give you a lift?
I don't want her to drive.
That's great you want her to stay safe and not risk herself driving! Just be sure to stay safe yourself and be aware, you wouldn't want to worry your girlfriend a lot.