Oxygen is found in 3 forms: nascent (O), molecular (O2, the most common) and ozone (O3). Nascent oxygen, due to its electronic configuration (i.e how many electrons it has and how they're spread out across its electronic shells) is unstable, and tends to quickly form bonds with another O, forming O2. This is also the case e.g. for hydrogen, which is usually found as H2.
You can find O in this form in some environments, in the upper atmosphere there is enough UV radiation to break up O2 into O.
I don't know if anyone is interested but there would be more versions too. Solid oxygen (red oxygen) at high pressure used to be thought of as O4, tetraoxygen aka oxozone. But if you look at it with x-ray crystallography it's O8, octaoxygen. Cool huh