The twitch!

You'd invited me in, I did firmly decline! Did not wish to sin, Or morals undermine! You do tempt me so, But I'm not that weak! Won't go with the flow, For real purpose I seek! Your lips so inviting, I'm starting to twitch! It's all so exciting, This seven-year itch! "Just once and once only," With brains I don't think! Marriage ends...sad and lonely, Barman, pour one more drink!