02 Passat check engine light/sometimes wont' start

I've had my 02 Passat 1.8T for a year now with no problems until about 5 months ago whent he check engine light came on. My mechanic (not VW) ran diagnostics and said it was the O2 sensor. He turned the light off, but it came back on two days later. It has been going on and off ever sense, but I hadn't had any problems. Lately, there have been more and more occasions when I'll run into a store or daycare and when I come out, I have to crank my car three or four times before it will start. Could these two things be related? I'm not a car person, just a great driver. Somebody help!

O2 problem will lower your mi/gal ratio. When trouble light comes on then there is a problem, and untill it is fixed, it will not go away on it's own, or it will appear intemidient.