The Musical HAIR has many themes including: The Age of Aquarius (astrology), hair, rebellion, drugs, politics, war (anti-war), coming of age, revolution, music, space exploration, and others...
Though I have seen it, I am not intimately familiar with the musical. Others may understand this better than I do....
The word DIVE has multiple meanings and slang usages. The meaning of IN THIS DIVE in the context of the poetry of this song could be purposely vague. A DIVE can refer to a bar, restaurant, cafe, etc. which is not chic. A DIVE can refer to a free-fall, such as one executes before opening a parachute or entering the water of a pool or lake, etc. It can represent the experience of immersing oneself in something quickly, deeply and fully....Here, it may well refer to a drug experience, such as an acid trip (which might be happening in a DIVE cafe or hangout...)
I hope this helps!