There is probably 1 of 2 things going on.
1 - The bladders are way over-sized, kind of like a bike tube. That way when the boat is inflated, all the air pressure is on the outside PVC and not on the welded seams of the Urethane AIREcell. If one chamber is inflated to rock hard pressure before any of the other chambers, it could take up 1/2-ish of the boat which would make it appear that one AIREcell is filling up most of the boat. This could be particularly true if an internal bulkhead is blow out, then one chamber really could fill up about 2/3 of a 12' boat. For reference, here is a raft inflation video we put together:
2 - The fused AIREcell is not out of the realm of possibility. That being said, we have only seen it a few times in our repair shop with heavy used outfitter boats and in early 90 boats because we didn't have a bulkhead system back then. For your AIREcells to have fused together they would of had to blown through the bulkhead and baked together in the sun. Blown out bulkheads don't happen often and are usually cause by years of repeated over-inflation.
3 - So what can you do now? Inflate all the chambers of your boat to 1/2 pressure and then top them off as described in the video. Does everything look right? If so, your well meaning boyfriend probably just over-inflated one AIREcell before filling up the rest.
4 - If one chamber really is inflating your boat, it's time to take a look inside. People tend to be intimidated by zippers but they are not THAT bad.
Here is a zipper video we put together:
5 - Take a look around. Are any bulkheads damaged? Is anything ripped? If so, give us a call at 800-247-3432 or direct to service at 208-991-5771. If you are feeling particularly adventurous, Here is a video on replacing baffles:
So, the good new, every piece of that boat can be repaired or replaced. If you don't feel comfortable opening up your raft you can awalys send it to us or one of our service centers. Let me know if you have any questions and keep us posted!