I too am one of those divers with a non-diving spouse. Interested in doing a liveaboard dive vacation on my own and am wondering if I'll be "the lonely guy" if I go on one of these trips.
As a single diver, I find liveaboards a great way to make sure I have a "buddy". If I don't meet someone with whom I am interested in diving, I can ask for one of the divemasters that work on the boat to dive with me. So far I've been fortunate to meet some really great people and wind up being long term friends with them
Are they mostly couples?
It changes from week to week. If you are concerned about there being other "single" divers on the boat, I would suggest that you call the office of the operation you are planning to go with and ask them the demographic makeup of the week you are considering
Will I be a social outcast?
Only if you are a social outcast on land