I have cancer and it really makes me sad that no-one takes it as seriously as I do
I can't believe they really don't care. Why don't you think anyone is taking it seriously?
My girlfriend said that cancer is disconcerning, she laughed about it
It is possible that your girlfriend is just feeling upset. It is bad to judge the reactions of others. Maybe you should talk to her about how you are both feeling.
Talking is not going to solve anything. I feel like she is not madly in love with me, she's just taking advantage in me.
Having a girlfriend that doesn't care about your health condition and isn't really in love with you is no good. Consider breaking up with her and focus on treating your cancer. You'll find someone more caring to be with I'm sure.