When married people get that twisted, pitying look in their eye and ask you why you aren't married -- or, worse still, offer lists of reasons why you are not -- it is time to say, "right back at you!"
Time magazine calls marriage a 'luxury yacht.' Remember what happened on the last cruise ship?
The cover of Time magazine asks, in big bold letters,...
To be single at heart, I think, means that you see yourself as single. Your life may or may not include the occasional romantic relationship, but you don't aspire to live as part of a couple for the long term.