One who is attentive, caring, compassionate, trusting, honest, open, commited, intuitive, helpful, handy, willing, receptive, and to borrow a line from a movie.... "One you can see yourself growing old with"... hehe
"commitment".... "Forsaking all others"... "Till death do you part".... "For better or worse"...
All of these are mentioned in the wedding vows.
No... swapping does not make things better... If one were to do a poll they would quickly find out that couples that do engage in these type of things aren't couples for long.
I personally am looking for that one special lady that can handle "together forever".
RE: Qualities of a truly nice guy.
Those are all just attributes I think a person looks for in a nice person.