Hi - I'm not sure what the expression "my morals got me on my knees" means, but to be under someone's spell is to be captivated by them/ in love with them.

Hi this is a song called Mercy by - Duffy. Here are the first 3 verses. Yeah, yeah, yeah Yeah, yeah, yeah Yeah, yeah, yeah Yeah, yeah, yeah I love you But I gotta stay true My moral’s got me on my knees I’m begging please Stop playing games I don’t know what this is But you got me good Just like you knew you would I don’t know what you do But you do it well I’m under your spell Th song writer is pleading with his beloved not to make him/her beg for love as he/she is so in love they will do anything. They are bewitched or under their spell.