。。
Let go of my arm. It hurts.
Literal
Arm [object-を] release-[emphatic-よ]. Painful [feminine-わ].
A softened demand to be released, paired with a justification. 放す is a variant writing of 離す, with slightly different nuance (放す = release, as in setting free; 離す = separate). 離して and 放して are both used but 放す emphasizes 'release from grip' while 離す emphasizes 'move apart'. わ is feminine assertion. 痛い is the standard 'painful, it hurts'.