To leave holiday early even if it will upset my dd?

It’s sounds like in the immediate term he has the care he needs in hospital and with his dad. There is time when you get home to address the wider issues and get the support he needs.

Your DD’s reaction is quite strong under the circumstances which suggests that your DS has taken priority for too long. He needs support but he also needs to know he can’t manipulate and control you when he fucks up by putting himself in hospital.

Stay and focus on spending time with your DD. She's done you a favour letting you know how overlooked she feels, ignore at your peril.

He did this intentionally.

He might be embarrassed in hindsight, although I agree he should have a chat with a professional re potential intentional self harm, but you flying back might make it worse. He is in the right place. Maybe take him out when you get back for a chat, his mindset could be different in a weeks time.

But make it clear his dad has to monitor him and not dismiss this.

Have you spoken to him directly?

How unpleasant to call op’s ds1 the golden child when he suffers from a chronic condition and is seriously unwell. It’s not as if op chose this situation. And many young adults with diabetes go through a rocky patch in managing their condition. This situation isn’t fair on any of them, the Op, her ds1, or her other dc. Causing her more guilt doesn’t help one bit.

I would probably stay but I would still worry about him. He is where he needs to be and has a parent with him.

It does sound like the poor mental health needs to be addressed though if he is suicidal. You didn’t go into specifics about why he did it over a girl, but if it was a way to manipulate her this needs to be nipped in the bud asap! I had an ex who would do this when I was a teen and it was awful!

No. You should stay.

What if it was caused by attention seeking to distract from his abysmal results?

Stay. DS is in hospital so is being cared for and I imagine they will take into account his mental health. He also has a parent present so it's not like he is completely alone.

Do you also have 2 other children? One of is obviously feeling extremely resentful and overlooked? This choice could have quite serious repercussions for her relationship with her daughter and grandchild.

I understand being worried about your son. However your DD's reaction tells me that this isn't the first time your DS has done something that has taken time and attention away from your other children.
I grew up with a brother who had a knack for getting into trouble with the police and or having a mental health crisis whenever something else was going on, whether it was a school event for me, parents going on holidays, a wedding. It was tiring as it went on until his early 30s. Any nice occasion had a good chance of being ruined because of him.
Your DS has his other parent so he's not alone. I wouldn't leave, not when your DD is clearly telling you your relationship will suffer.

Mum of a 20 year old with T1D and if he was in hospital with DKA I would be there no questions asked. Especially if triggered by a mental health crisis.

I used to work on the endocrine ward and DKA can be life-threatening, but as he is now on the ward getting the treatment required to correct it, he'll be fine. I don't think you need to hurry home ...if he's arguing with his dad he's probably ok!
I would say however that we did have a few regular young diabetes patients that had mental health issues, some even using insulin to self harm. So your son's dad should not be so dismissive.
But for now, your boy is in safe hands and his dad is there so enjoy your break

From the sound of it your relationship with your daughter is already on shaky ground over your prioritising your golden child ie ds1.
If you chose to prioritise your son and go home early it will most likely be the final nail in the coffin of your relationship with your daughter and grandchild.
Your son is in the care of his father and doesn't need you rushing home aswell

Your son is under medical care.

Stay with your daughter. Your daughter just told you how frustrated she is by the special treatment you give your son because he's got Type 1. Leaving now will bring more resentment into your relationship.

You need to do some reading on glass child syndrome.

I’d stay.
Realistically what do you think you being there will achieve?
Do you know what you DD meant by her comment, does he have form for suddenly needing you during events that are about his siblings?

Stay. He’s got a parent and he’s being treated. I don’t think you’ve given your daughter enough attention or love - she’s telling you that! Listen to her!

You need to try and give some of yourself to your daughter and grand daughter. It simply isn’t ok to choose your son time and time again. It sounds like this is a crossroads and your choices here will count.

I’d stay. He is not on his own, he has his dad. He is safe in hospital. Your dd deserves your time and attention too as it sounds like she hasn’t had much of it due to her brothers illness.

Let his dad take the strain. Dad's are as much patents as mums so let him step up here. But I'd explain to dd that this is serious. How she react if you flipped her off during this kind of health crisis? Your allowed to care and be upset

Sounds like there's a history of him being more important than the others?

He's an adult and he's not alone. YABU.

It’s attention seeking at its finest. I’m assuming it’s because his dad is (rightly) angry he bombed his a levels and destroyed his future. So he eats a load of sweets in order to end up in hospital and his mum rushing back to his side, because she goes easier on him than his dad.

I completely understand that you’re terribly worried about him. And you’re really stuck between a rock and a hard place. I would probably stay right now but keep in close contact and you can always leave later in the week if his condition deteriorates. His dad and his brother are with him so he’s not on his own. Sending hugs

Trust the hospital and his Dad. It’s a summer holiday. You haven’t emigrated to the moon.

Stay but call him, facetime him see how he is you will feel better when you've spoke to him