Is it really "shallow-ness", or is it fair in the game of love and lust? (GUYS ONLY PLS :)?

Shallow. No such thing as "fair-game" in that context. He should enjoy you and like you the way you are, unstable weight or not, and unless you become quite obese when you're at the height of the yoyo weight, why the hell does he care? Anywhere between sizes 6-10 and sometimes 12, women are very sexy.