Why is cat urinating in the house?

Hi Dr. Marie,

Recently, my one cat Habibi has started urinating outside of the litter box. It has been happening for about a month, but generally only once or twice a week. I know it's Habibi because my roommate keeps catching him do it, and he acts more cooly toward me than my other cat does when I return home. The problem is, he pees right outside of the litter box, either on the litter-catching mat or the rug underneath the mat/box Once, he peed on our kitchen rug, but I was watching him do it and stopped him.

It seems to happen when I need to leave the house, and especially if I need to be gone all day or overnight. The cats are never alone overnight, though, because my roommate is here if I'm not. She doesn't let them in her room, though, and they're usually allowed in mine.

The only things I can think of that maybe relate are (1) the fact that I was home much more frequently during May and June because of a work schedule change and a month off of school, and (2) they seem to get very upset when we have more than one or two other people over. When Habibi peed on the kitchen rug in front of me, it was the day after we'd had a few friends over the night before. A couple of friends slept in our living room, since they'd driven a long way to visit, and the closet with the litter box is attached to the living room. The cats hid under my bed all night, only coming up to sleep with me and then slink back under the bed. The day after this, I was gone for most of the day. When I came home, he started peeing on the rug. The other times he's peed, though, seem to correlate with the times I need to leave for a while after spending more time at home.

I'm willing to take them to a vet once I actually have a day off, but I don't know if it's medical. If it were an infection, wouldn't he be peeing in multiple places, doing it more frequently, or acting sick and lethargic? I don't know if it's anxiety related or if he's just mad at me, but it can't keep happening. I'll be working 70 hour weeks once the fall starts, and can't have him peeing on the floor every few days. I don't want to get rid of him, because my other cat, Falafel, is his littermate, and they're very bonded. Falafel is just more easygoing and loves most people who come to our apartment. Habibi is more standoffish and only seems to let me pet him, and chooses when he wants me around (i.e. while I'm sleeping, he's started rubbing up against me and curling under the covers with me).

I'm sorry to give you so much information, I just want to make sure I give you as clear of a picture of what's happening as possible. Thanks so much for your time. I hope you can give me some tips! I've been reading about the feliway diffuser, but didn't want to shell out a ton of money (I'm a grad student, after all) unless it'd been recommended by someone other than an online reviewer.

Take care,
Emily