Hi
HUGS
Please take a deep breath and see what the examining vet finds and take it from there. It doesn't necessarily take an exotics vet to spot the obvious; an experienced general vet is perfectly competent to do that, as I know from my own local vets. If it is an infection of the lymphatic system, then antibiotic treatment is an option. If it is the immune system/the body failing, then yes, ayou may be faced with cutting short a process that has is already underway.
But as long as you are making any dispositions with Beanie's welfare interests upmost in mind, then you are not failing him, whichever way things go. And that is what counts when all the dust has settled.
It is perfectly normal that your thoughts are racing and that you are in an emotional upheaval as the result of the sudden overnight deterioration. It's the sheer shock you could not brace for and also your grieving process waking up with a real bang.
Please try to set all that aside and focus on Beanie for the next few hours. You are doing all the right things but you have to ride the tiger wherever it takes Beanie and you. Overthinking and doubting yourself won't help you; you can work through all of that later on once you have dismounted the tiger. Right now, make sure that you keep a firm grip on top of the tiger and that you cradle Bean safely, be honest with yourself and listen to your gut when you need to - that is what really counts right now.
You cannot control the tiger but you can stay fully with Beans in the moment in order to minimise any discomfort for him. Give him your love but without any of your desperation and without any smothering; just a light green, warm, supportive touch - as if you would carry him ever so gently on your hands over a warm pond. Half-heat a snugglesafe so it is just comfy but not hot and reheat at need but give him the option to move away when he is overheating.
Try not to get lost in your emotional baggage and lose your grip over all the what ifs. Just be there with Bean and in the moment. Most of the what ifs and potential avenues usually turn out to be irrelevant anyway. But you being there with him is what counts right now and where you can do something constructive. You will always find it in you to be strong for somebody you love; hang onto that rocky core inside you and use it to support Bean, whatever happens.
My thoughts are with Beanie and with you in the coming hours.