Mama, just killed a man. Put a gun against his head, pulled my trigger, now he's dead. Mama, life had just begun. But now I've gone and thrown it all away.
Mama, ooh, didn't mean to make you cry. If I'm not back again this time tomorrow: carry on, carry on as if nothing really matters.
This lyric is rather perplexing because the meaning of the lyric is not literal. It's more a metaphorical death. The singer, Freddie, is probably talking about killing some part of himself and reinventing a new life. Perhaps this lyric is about getting rid of straight self and starting life a bisexual man. This new life creates a lot of tension in his life particularly with him mom and family , hence the other part of the lyric.