JesseC dixit:
apparently it may mean "more then ever mine"
It is tempting to translate mes as mine, but I am not sure that it is correct.
For example, from "Le Fresne"
Li sires dit: "De ce sui liez;
Onques mes ne fui si haitiez.
The lord said :"????
I have never been so happy"
Li chevaliers qant il le sot
Onques mes si grant joie n'ot
The knight when he knew about it
Was never so joyful
Le paille esgarde sor le lit,
Onque mes nul si bel ne vit
She saw the cloth on the bed
She has never seen one so beautiful