Es kommt mir vor, als wären seitdem Ewigkeiten vergangen, so viel ist inzwischen passiert.

I have some trouble to understand this. I think it means:

"It feels to me as if eternities have passed since then, so much has happened in the meantime".

Is this correct? Why do we have "wären" there? I think I need to refresh my grammar about "wäre"/"hätte"?