Genesis 2:18 ASV

This verse says very little about whether or not singles should feel lonely.

First, it is God and not Adam speaking; for all we know, Adam may have thought it was perfectly fine to be alone. Second, despite how it's usually quoted, almost every English translation says "the man," not "man" - this verse is about Adam, not about humanity in general. Third, the primary sense in which Adam was alone was *not* that he was unmarried - it was that he was the only human being on the planet.

Instead of drawing conclusions based on this verse that it's OK to feel lonely, I'd recommend looking at what the rest of scripture teaches about delighting in God in all circumstances. I want to get married as much as the next guy, but I also want to glorify God by being satisfied in Him while I'm single.