I hope you find out what it is soon so he can been treated, I'm so sorry he is going through so much and you have the worry of it. If it is EK, my cat had 1% cyclosporine drops, once a day and her eyes cleared up in a matter of a week and remained clear. Please keep us updated.
Is the litter scooped after every use, some cats don't like using a litter tray if it's dirty. As for the diarrhoea, you could try adding pure pumpkin, no additives, to her food or try S Boulardii, I have had a lot of success with it.
It could well be stress related that's causing him to block. What exactly did the vet find, any debris in the bladder, what was the blockage?
Have a look at D-Mannose and Cornsilk, they help my cat with stress related UTI.