Apologies, I was trying to spare some details so that I didn't end up in a TL;DR scenario. I can be a bit long-winded when I write.
In early March (specific date I don't recall) he told me, "oh, just a heads up. I am looking for a job and might have to move for it. If I can't find one, I'm moving back in with my parents at the end of the summer." About a week later, he additionally commented, "I might actually move back home at the beginning of summer to save some money instead of stay here all summer, unless I find a job in the area."
I never heard anything else from him. I came home from work on April 15th and he was loading up his vehicle. I asked him if he was going home for the weekend, and he said he was moving out this weekend and he should be out by Sunday. I didn't really press the fact that he was moving out without much heads-up on the spot, I was surprised by it. I went away for the weekend, and when I got home Sunday, all his property was removed and the keys were on the table. I called him to discuss the outstanding utilities, and he said he acknowledged he owed, but also mentioned that I need to refund him rent between April 18 and 30 since he wasn't living there anymore. I said I wasn't given any kind of notice you were moving that weekend, so I need time to potentially find someone new, and I don't feel I owe him any refund and that honestly I wouldn't be surprised if he still owed some rent. He said that we will have to talk some other time when I am feeling more reasonable, and we haven't been in touch since.
Based on the things you and adjusterjack have been saying, things I was told on another forum, and my desire to just move on from this, it's sounding like I shouldn't push the improper notice issue, and try and (best case scenario) get him to drop his claim of a refund and collect the utilities. It all really depends on how adamantly he intends to pursue his belief that I owe him the refund, I might end up having to just write off the utilities in the interest of getting it over with. The amount I would "owe" him, assuming I considered his refund claim valid, would be less than $100.00 when subtracting out the utilities, and I don't see him pursuing that amount in any fashion.
Thanks again!

