However, with weddings costing an AVERAGE of $196 per guest, not every couple feels like doling out "and Guest" to each and every one of their single friends, and sometimes take great pains to avoid the extra mouths to feed.
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.