Unsure whether to put Phineas to sleep

[Missile.x]

Hi, (this is a long thread because I feel medical history is probably relevant to my question, sorry)

I'm basically posting this because I'm experiencing a very difficult dilemma. Phineas is 2 year old syrian hamster and about 6 months ago I took him to the vet because he'd lost some hair on his bum and I was worried. The vet said he probably had cushings, but seemed healthy otherwise so not to worry and told us what vitamins we might give him to help best we could. A little more hair fell out but other than him peeing a lot more than usual he seemed fine. In fact, over the next few months his hair actually grew back making us think the diagnosis could even be wrong.

However, about a month or so ago I noticed his abdomen felt funny. At first I thought I was imagining (as I am a worrier), but within a few weeks it was clear something was very wrong. His abdomen was getting increasing swollen, squidgy to touch, not hard. I immediately booked him into the vets thinking this was it and he'd need to be put down. However, they said while they couldn't pin point a reason without an X-ray (which at almost 2 years could be risky) he seemed bright eyed and he was still eating and drinking etc. the vet said there was probably no need to put him down at this stage.

At present, Phineas's abdomen has really gotten very large, especially on one side. His eyes are frequently shut together when he's awake and outside of me nagging him with eye solution he cannot see a lot of the time. He sleeps most of the time and his abdomen is making it really quite difficult for him to move around, but he is still eating, drinking and fairly inquisitive. I am very unsure what to do. I don't know whether it would be kinder to take him in and have him put to sleep or whether I am taking comfortable life from him. He's had a good innings and I can't imagine having an abdomen that huge (so big his ridiculously large testicles have dropped even lower on his body) can be comfortable. But at the same time, who am I to rob him of life if he's still getting by?

Does anyone have any insight? I have thought this through over and over again but still can't reach a conclusion. I love him very much and I just want what's best for him.