Your girlfriend doesn't know why you're so unhappy. She knows what she does when she's unhappy though... she knows that cum in her mouth, down her throat... that's what makes her happy! So she suggests you do that and instructs you.

And honestly, she says you'll be happy about it regardless. It's like any health claim really. Even if it's just a placebo effect, it's all worth it and valid. You'll be happy in no time!