Roman, yes, the thought that I may have done something to hurt or offend him crossed my mind. Specifically, before he arrived I was talking and dancing with another guy. Other Guy couldn't remember my name and, to amuse myself, I told him I'd make out with him if he could remember my name. I was confident he wouldn't remember it (he didn't) and I wouldn't have to make out with him. Wouldn't have anyway. I told Neighbor this story when he arrived. I honestly didn't think he'd care. I was talking to Other Guy again when I watched Neighbor walk right past me and out the door. We do not have any kind of agreement on exclusivity, I wouldn' even say we're dating, plus my ex couldn't have cared less who I talked to at the bar, he didn't know what it felt like to be jealous, so I'm not used to being cautious about those things.
Also, I didn't really think he liked me enough to get jealous over me. Anyway, long story short, I think there's a possibility he ditched me out of anger or jealousy. Still, really no way to know without asking him...

Sometimes we go and have a drink while the boys are in hockey, so there may be an opportunity for the talk tonight, which is majorly why I'm here.