Jen have you had him checked for diabetes? I mention this only because Trevor was diagnosed back in July after I found him peeing outside of his litter box on three occasions after never doing it before in his 10 1/2 years of life. Then I noticed him drinking lots of water. He is doing just fine now thankfully. At first I thought "oh no, I have a behavior problem brewing here" but after blood and urine testing there was the cause. (((hugs to you and sweet Sterling)))