I see so much people do 3:1 Str Dex so there is no point in con ?
Oh trust me, there is a point in CON and they will definitely feel the pain later when magical types of tanker-like ranged mobs are almost everywhere 
there is. but you won’t really need it until 165+.
im a pure rogue r3 so what i should do ?
Forget Dex if you’re going Rogue.
Go all or nothing on Sneak hit.
I did put points on dex and str (1 to 2.5) and little bit con. But not sure if my dex will be too high once I start using gems.(sneak attack + swift step bonus+backstab bonus = approx. %160 increased crit rate).