TRIGGER WARNING BEFORE YOU PROCEED: MENTION OF DEATH.
You are close with the cast of the freak circus. Not exactly dating, but not exactly family either - just close. They trust you, you trust them. They protect you, you protect them. But you're NOT a part of their family. More like a friend, a pet human, amongst the terrible humans out there (and there is A LOT). However, they did their routine checks on you and find out you have died.
(You can choose your own cause of death)
To say he's devastated is not even close. To say he would be inconsolable would be more accurate.
He would be like that for a long time, a few decades maybe, maybe longer. But eventually, he'd realize that you'd want him to be his normal self and not mopping around all the time.
He's gonna say and pretend like it doesn't affect him. However, when he's alone he would probably be crying his heart out. Probably.
He would definitely bother Pierrot and the others more as a coping mechanism.
He would cope with it by doing more work.
I don't think he would do anything else besides more work. He would find work for himself to do if he has to and if he runs out of work to do, he would just write.
He would write letters to you specifically. Talking about his day and how he's been doing since he's lost you.
He would definitely over groom himself. It wouldn't be a conscious thing either.
He would also try to convince himself that he's unaffected because you're human and your death was inevitable, but really deep down, he's more affected than he cares to admit.
He would cope with his grieving in a way that is actually healthy and beneficial, since he's a doctor, he would know that stuff.
He would also try to help the others that need it - more specifically Harlequin and Pierrot. Jester would just decline the offer and Ticket Taker would just hold up a box of hand written letters.