Larb

Bonjour, I am a beginner in learning French. I came across a grammer issue that frustrated me: When I want to say ‘I love you’, I may use ‘Je t’aime’ , in which I (Je) become the subject of the sentence. When I want to say ‘I miss you’, I found that it is suggested as ‘Tu me manques’, in which you (tu) become the subject. why is the difference there? Merci beaucoup!!