Whether you were in a relationship that no longer exists, have friends who can't take time off to currently travel, or just prefer to be alone, being along should not be a deterrant for not cruising. As a matter of fact, traveling solo has many benefits. Here are just a few:
Life's an adventure. Why should being alone not be. You may not have the safety net of a few friends, a wing man/woman, or family members, but cruising afford you the opportunity to meet like minded people like yourself. Keep in mind that everyone one that ship, including those traveling stag are hoping to visit the same destinations that you are on that very same week. Make certain that you sign yourself up for ship board activities, hit the bars, schedule some shore excursions and lounge by the pool. Make friends with the bartenders at your favorite watering hole on the ship.
Safety first. For the most part, cruising is safe. It's one of the few vacation opportunities where it's actually safe to be along and not have to worry. Traveling on land as a solo person, I've heard, is far more dangerous than at sea.
Maximize your time alone. By this, I mean, go do something that your friends would not be interested in participating in even if they were traveling with you on the same week. Go get a massage. I have a friend who hates massages, so when we travel together, my spa time cuts into our bonding time. Take a cooking class, go play bingo, find something to do that you'd normally not do because you're entertaining your friends on vacation.
Remember, you may be sailing alone but each one of those passengers you pass in the hallways, sit next to on the lido deck or at a bar, is a new potential friend. Eat when you want, what you want. Sleep as long as you want without having to get up to meet someone at a designated time.