Being single is a relationship or marital (status) one lists on a form.
A person can have 5 dates a week with 5 different people and still consider them self to be "single" or "free" and not in a "committed relationship". Lots of "single" people have "friends with benefits" or "booty calls" with people they know while they're still seeking "Mr. Right" if you're talking about dealing with physical loneliness.
Loneliness from a (mental) point of view is a feeling of being "disconnected" from everyone in the world at a particular moment. It's even possible to be in a room crowded with people or even be married and yet still (feel) alone/lonely. It's a feeling that "no one gets me". Keeping things in perspective is the key.
Everyone you admire or believe has it all together also have moments of loneliness, feelings of insecurity and doubt. Understanding one's loneliness is temporary can keep it from developing into "depression".
Focus on things that bring you joy or read books that inspire you, go to the gym consider joining some hobby groups on Meetup.com, have a night out with the girls, take in a movie, or hang out with some family members. Develop some "me time" activities to spoil yourself.
Anyone who sincerely enjoys their own company rarely feels loneliness.
Being physically alone on a planet with 7 billion people is an intentional act. There are tons of places to meet and engage with other people. You'd have to deliberately withdraw to be alone.
If you actually want to be in a relationship but are avoiding situations where you could meet new people then your loneliness is by choice and it's the equivalent of going on a strict diet.
What helps people to maintain self-discipline in those situations is they have an "end goal" that is bigger and better than any temporary moment of satisfaction they'd have by breaking their promise.
The goal has to be big enough in your mind to justify the sacrifice.