I do not believe in happiness, but you.
直译
I would rather believe in you than to believe in happiness.
“would rather。。。than。。。”有“宁愿。。。而不愿。。。”的意思
I believe in you instead of happiness.
也可以译成“我相信的是你而不是幸福”
It is you but not happiness that I believe in!
这个语气比较强,“it is ...that...”表强调
我不相信幸福我相信你。
I don't believe in happiness, but you.
I never believe the happinese,I only trust in you.
尽力了,好不好就看你了
i don't believe in happiness,I believe in you
i trust you,not the happiness!