I see the problem. He has swim bladder disorder, which is caused by poor water quality and consipation. He needs to be in a minimum of a 2.5 gallon tank, heated to 78-80* F. Right now, in a 1 gallon, you need to be doing 100% every other day at the very least.
You can buy a 2 gallon sterlite tubberware for a dollar or two, and fill it halfway up to 1 gallon so he can reach air easily. To heal him, add one teaspoon of epsom salt per gallon, keep the tank in a warm spot, and do 100% water changes once a day, every single day. No slacking, because water quality is the key to his recovery. If he heals and can swim well again in less than 10 days, then that's great. Stop the salt use, and you can go to 100% every other day (I still recommend 100% every day however). If he isn't better by 10 days, stop the salt use, but still do 100% every other day.
Also, very imporant, presoak his pellets all the way through before feeding (2-3 pellets twice a day), this will help reduce the chances of constipation.
As soon as possible or when he is healed, buy him at least a 2.5 gallon tank, and a heater (5 watts per gallon). If you buy it while he's healing, get it up and running, and have his tubberware floating in the heated tank (it'll keep his hospital tank warm as well, which will aid recovery.)
Once he heals and is the proper conditions, chances are he can have another 3 to 4 years with you seeing as bettas can live about 7 years.