need advice on properly kicking out room sharer out of my home in CA.?

Currently I reside in my own 4/3 bedroom home and rented two spare bedrooms to outside renters. One of the renters, rents two rooms from me and operates his computer business from my home. He is a network engineer. He started to rent from me Jan. 2012 and I made it very clear that this would be a month to month arrangement (in writing) since I was dating someone and most likely by the end of 2012 I was going to have her move in with her children. I gave him notice on Nov. 4th 2012. I told him that I understood it was end of year and before holidays but I was giving more than 30 days notice to vacate my home by Dec. 31st. 2012. He had paid first and last month's rent when he moved in, but I gave him an incentive by offering to give him his last months rent back if he moved out by Dec. 1st. $800 by Dec. 15th, $600 by the 22nd and nothing by Dec. 31st.

During the month of Nov, he wasn't really looking, but then in Dec. he started to look, but always seemed like the places were too expensive, didn't allow dogs, etc, etc. The excuses are piling up. Before the holidays he told me that he found a place but he cannot move in until Jan. 15th 2013. I told him; "Fine, but you'll have to pay me for two weeks that you remain."

I just got back from vacation yesterday and he has a new girlfriend and the way he is acting it's like he's putting the "move" on hold or something. He hasn't mentioned one iota about moving out and in fact is acting like he's going to try and continue to stay and give excuses as to not being able to find a place.

I plan on serving him a 3 day eviction notice on Jan. 3rd. I wanted him out by Dec. 31st, but that doesn't look like it's going to happen now. Since I live with the guy, I don't want any undue stress living with someone you are trying to kick out, so what are some things I can do?

For example, if I only accept half the rent for the month of Jan. and he doesn't move out by the 15th, I think I'm screwed. If I accept the full month of Jan. rent, then that would imply he has until the end of Jan. to vacate. Or can I change the WiFi passwords or shut of the internet on Jan. 15th if he doesn't move out by the time he agreed with me? I know if I did this, it would severely hurt his business and he'd probably get more serious about moving out. Is this legal considering the original rent included utilities and wifi?