That's awesome that you are being proactive and have planned how you will handle the pet sitting thing when it comes up.
I think it's a huge help for us to be prepared with a "script" and not be put on the spot and us stuttering for words.
I "lost" some friends when I began to make better choices for myself, but I also strengthened my relationship with myself, and it's important that I be my own best friend first. I also improved as many relationships as I lost!
the thing is healthy boundaries work BOTH ways! When I respect my own I am actually being more respectful of other people's boundaries as well. And I am freeing them of the burden of defining me and myself of the burden of trying to shape myself to fit their definition.