No, you don't have to tell them, but make sure they can still contact you - getting a relative or friend to collect your mail and forward anything important to you will work.
Living together is good proof that the relationship is genuine, so if you don't tell them you are going to the Philippines now, still collect evidence that you are living with her - joint lease, joint utility bills; if such things are impossible, then an affidavit from the landlord, any roommates, or her family stating you are living together; bills for things purchased together for the house; lots of photos. She can then show this proof at the interview. The VO will probably ask for proof of contact since the application was filed, which usually means things like phone bills, emails, letters, proof of visits. In your case you will be showing proof of having lived together - which can include the proof of the visit, such as the plane ticket and boarding pass, passport stamps, hotel/restaurant/activity receipts.
The VO will then probably ask you to prove you are going back to Canada.