[VivianKJean]

sweetheart, you need a bigger tank (at least 2.5 gallon but more is better) and a heater! Betta's are tropical fish! They need water that is at a constant temperature between 78-82 degrees but most people find 80 to be the best. room temperature is def not warm enough, not to mention room temperature changes so much throughout the day.
like aselvarial said you would be needing to do twice a day water changes with a tank that small. even with a 2.5 gallon tank you need to do a water change twice weekly (find doing one 50% and one 100% per week is good).
Get a new tank WITH a heater ASAP. You might also want to consider a filter. A sponge filter will be fine.
He is probably stressed because his water isn't in good condition which is also making him sick.
What type of pellets are you feeding him? how much a day? Omega One and new life spectrum are the best.
you said you want him to be happy, then you NEED to take care of him properly.

 

[VivianKJean]

Lol, not my list of questions, its what they ask for in disease. In half a gallon, ammonia builds up fast. Daily water changes would be best. Also, if you plan to upgrade him this weekend, here is what its said on here is the minimum. A 2 gallon tank and a heater. I loved the aqueon mini bow 2.5 but it was on sale for $20 when I bought it. Until you upgrade him, do daily water changes and try to match the the water temp. Also flakes can cause bloating and are harder to get out. Stick to his pellets for now. Use a turkey baster to clean out any leftover food (or in the case of the small tank, feed before water change) He will probably stay stressed until you can upgrade him, but doing daily water changes with a good water conditioner (which I'm assuming you already have) will at least keep down the ammonia

I have 2 of my fish in the Aqueon mini bow 2.5 and they are doing very well. They also have one thats 5 gallon. You still have to do water changes more than once a week. I find one 50% and one 100% a week is the best, unless they are sick and then i do more frequent water changes.

 

[VivianKJean]

YOU NEED A HEATER. It was said multiple times in this thread. Betta's are tropical fish. You need a heater to keep the water warm enough. Get a GLASS thermometer. The stick on ones are unreliable.
read myexplodingcat post on this thread. Everything is said perfectly.
Just because you are a college kid doesn't mean you can miss treat a fish. Im a college student too but all of my fish are in AT LEAST 2.5 gallon tanks.
in terms of decor - get silk pants (not plastic) and just make sure whatever you get you make sure there isn't any sharp edges (run you fingers ALL over it, inside and out) and soak it before you put it in his tank to make sure there aren't harmful chemicals or paints. there a tread on the forum and lists dangerous ornaments
He is probably swimming away from you because he is stressed and not happy.
Honestly I hate to be this rude but if you weren't planning on doing TONS of research about bettas and what they need before you got tone then you should not have gotten one in the first place.
They are a big responsibility and way more than something cute to look at.