Bought a 2006 Honda Civic ex about a month ago, the check engine light came on and it was throwing code p0133 o2 sensor slow response?

Bank 1 sensor 1. Now I checked again and it's a P0171 code as we'll System Too Lean Bank 1 . My friend looked at it and said it's my oxygen sensor. Could that be the reason, and is that way it threw the other code as well? The car runs pretty good, does guzzle has a little.

A P0171 can cause a P0133, not the other way around. Your friend doesn't understand how modern engines work. Fix the P0171 problem first. Then see if the P0133 code comes back

Once again, check for a vacuum leak with a smoke machine. Check for a bad EGR valve.

I'd replace the Bank 1 front 02 sensor first. The person telling you that the P0171 code can cause the 02 sensor code in this case is wrong. The P0133 code is for a slow responding 02 sensor so the 02 sensor is not working right.
You may still have a vacuum leak OR MAF sensor that is causing the lean condition. If you're lucky the 02 sensor is the cause of the lean condition too.