Thanks for the messages, folks.
'Never' is indeed a long time but I'm really am a serial monogamist at heart. My wife and I have been together 15 years (10 years married); I was with someone for a year or so before that (more of a 'friends that fuck' thing than any intention of a long term relationship); and before that I was with someone else for 15 years.
Three partners in 31 years. Not exactly a stud muffin. I have a pretty strong erotic drive - I just want it to share it with someone I really care for.