You are the most important person in my life,but I think ,you don''t care about me .I 'm always feeling tired,so I gave up.
其实前面几句也可以用过去时,但考虑到这些想法现在可能仍存在于你的心中,所以我用了一般现在时.如果那个人对你来说已经不是最重要的了,那些想法也是曾经的,可以改成这样：
You were the most important person in my life,but I thought ,you didn''t care about me .I was very tired,so I gave up.