Identifying Betta depression

Question
So I've had my Betta, Cadmen (hi, me again.) since last August, and he's been doing reasonably well. Though his tank is rather small and likely lacking in necessary components, I might be getting a job soon which means that will be taken care of soon enough.

However, I'm noticing Cadmen is acting a little odd. If I move too quickly, he sometimes 'jumps', jerking quickly into the back of the tank, usually behind the fake seaweed I put in, and his fins are often shut/contracted. (He'll often jerk away when I make movements above his tank, like dipping my fingers into the water and such, but I figure this is normal) Where he used to have his fins open, and didn't mind me moving rapidly, this new behavior worries me.

I've been putting a drop of two of fungus medication in since the time I thought he might be getting fin rot (and recently, when I saw a white ring around one of his eyes); so I think that may be contributing to the cause of the jumpiness, but otherwise I think he might be depressed.  

I admit, Cadmen's tank is located in my room, where I am often not in it, so most of the day there is nobody in my room save the mornings when I get up and at night when I go to sleep.

I'm starting to wonder if this absolute lack of activity in my room is causing him to become lonely and depressed.

Can you help me any, or am I just being a paranoid owner?

Answer
Brittaney,

 The smallest size tank that a Betta can live in is 2.5 gallons. If he is in anything smaller than yes his tank is too small. The first thing you should do is get him a heater. He is a tropical fish and needs warmth now more then before since the weather is getting colder. Set his heater to 82 degrees. If his water gets too cold he will start doing everything you are describing.

"his fins are often shut/contracted. (He'll often jerk away when I make movements above his tank, like dipping my fingers into the water and such, but I figure this is normal" This is  NOT normal at all. He is displaying clamped fins and could be for a few reasons. Never add any medication to the water unless you know exactly what is wrong.

Betta's are very sociable and like to have their "pets", which is what we are, to give them as much attentions as we can. Since I have 11 adults, they keep me quite busy. While I am tending to water changes and feedings or anything else I have to do, I talk to them. They dance for me and make me bubble nests and even talk. I have a couple that I have taught to jump through a ring. If it is possible, I would relocate him to a room where you hang out the most. If he is in a small tank it should be easy to move him and them take him back to your room at night. You can try placing a mirror in front of his tank every day for about 15 minutes. He will think it is another male Betta and he will flare out when he sees himself. This cuts down on the depression quite a bit. The sooner you get him the heater the sooner you will see a huge change in him. As far as the nervousness you mentioned, it is because he doesn't see you often enough.

I think once you get him the larger tank, the heater, and interact with him more you will see a much healthier and happy Betta. If after you try all this and it doesn't help, or he gets worse, let me know.