Sounds like he might unfortunately...good news is it is curable...It takes a different amount of time for each fish...Just Go to your local aquarium and fish shop and ask for their best medication for fin rot. I cant remember the one i have always used but they will be able to help you. I always leave my medication in the tank for as long as possible. Do not change the water. Just top up the tank as it evaporates. The medication i use turns the water a blue colour. Put him in a small tank..anything less then 5litres as you then wont have to use as much medication. Once you are sure that the fin rot is gone you can then change the water in the tank.

First of all, NEVER, EVER allow someone else care for your fish while you are away. They can NEVER care for your fish like you can. Unless they know how to care for fish.

Put him in a 2-1/2 gallon aquarium. It's only $14 at PetSmart and with a small heater you betta will thank you for it!