The two sides mean a river.
Ancient Chinese believed the river never stops flowing, and it is endless going forward which is Forever. A person in the river could mixture into river to become part of the river which is forever alive.
Chinese proverb says "与山川同在，与日月同辉“ - With mountains and rivers, with the sun and the moon, which is forever.
The bronze script for character Forever is
The middle is a person, the river flow on the sides, similar to the shell bone script.
The small seal script for the character is
The middle person has the flow shape, and the two sides are water flow, which is similar to small seal script Water as below
The clerical script for the character Forever is
The person in the middle could no long be recognized easily.
Let's compare it with clerical script of Water
The bottom parts are identical each other.
Its Pinyin is Yong3.
Chinese normally say "永远“, which is Forever. 永 - forever, 远 - far. 永 is used in formal writing, specially poems.