Yep, it's a metaphor. The "snake" is not reptilian, but human -- in a way. It is a song about an abusive or unfaithful partner. This woman with a gentle heart meets a good-looking fellow who's in some sort of bad way. She helps him out, they fall in love, and as soon as the man gets his life in order, he does something to hurt Lady Gentleheart, (abuses her, cheats on her) then justifies it by saying she knew he was the way he was when the relationship started
Yep, it's a metaphor. The "snake" is not reptilian, but human -- in a way. It is a song about an abusive or unfaithful partner. This woman with a gentle heart meets a good-looking fellow who's in some sort of bad way. She helps him out, they fall in love, and as soon as the man gets his life in order, he does something to hurt Lady Gentleheart, (abuses her, cheats on her) then justifies it by saying she knew he was the way he was when the relationship started