For past week, when i blink left eye , the cheek immediately below it often pulls a bit tighter as if on the verge of a twitch. what could cause this?

Fasiculation: It may be a benign condition called a muscle fasiculation, which is like a "twitch" that you area bout to feel. Stress, minor fluctuations in electrolytes can cause these, and at times, there is no known cause. Rest assured though, this is benign. Rub the area, stay well hydrated and the issue should resolve on its own. Best wishes.

Eye twiching: If you mean the eyelid blinking of fluttering, it my be myokymia due to stress or simply dryness of the eye. If the eyelid(s) contract fully, and is very noticeable it could be blepharospasm or hemi-facial spasm. See an ophthalmologist. Most likely stress related.