I edited the pics a bit and made them brighter but still couldn't really tell much from them. However, it sounds like it could be a cyst (soft and squishy) or the fish is fed way too much. Probably a cyst tho and there really isn't much you can do without spending a lot of money on it. If the fish was cheap then I would just leave it be, and as long as it keeps eating there shouldn't be any problems.
If there are other catfish in the tank then watch them for any similar lumps. It's unlikely to be a problem tho because cysts don't get spread from fish to fish and neither do tumours. Internal bacterial & protozoan infections can spread from fish to fish but they usually kill the host fish within a short period of time (usually a few days to a week of the symptoms developing). If the fish has had the swollen area for a month or so then it won't be an infection and is unlikely to spread to anyone else in the tank.
If you can post a few more pics we might get a better look at it. Also check with your boyfriend and see how often it gets fed and if it eats a lot. It might just be a greedy guts and pig out on food, thus causing the big fat belly area.
Also does the swollen area appear to be more on one side than the other, or is it even on both sides?