Hi Kristie,
I'm really sorry to hear about your partner's diagnosis at such a young age. My mum was diagnosed at a similar age and I'm the oldest of two children. I'm a carer for my mum now in my mid twenties.
If I could give any advice at this stage, it would be to get social workers involved as soon as possible so you can possibly get a hand with his care. From the emotions you describe, it sounds like you are close to a carer breakdown. Mention this to the social services, as this will set an alarm bell ringing for them and they may be quicker to help, act, and make sure your partner gets the care he needs.
The following factsheet that Alzheimer's Society provides can help you understand how to get the ball rolling: Assessment for care and support in England. This can be found on the Alzheimer's Society website under the "Get support" tab. Unfortunately I can't send links at the moment as I haven't posted enough.
Depending on where you live, you can call them directly or get referred through your GP.
It's hard to think about these things when your loved one has just been diagnosed, but when you're ready it might be a good idea to read through the Planning Ahead booklet - also available on the Alzheimer's Society websit, on the publications page which is under the "Get support" tab.
When my mum was diagnosed, me, my dad, and brother had to become her Lasting power of attorney (for health and financial) as mum doesn't have the capacity to make decisions for herself anymore. It's good to get this done sooner rather than later as it can cause problems later on if you don't have this.
If you're struggling, it's always worth calling the Alzheimer's Society support line. They've been a big help to me and the past, and depending on where you live might even be able to arrange a visit or meeting.
Hope you're all as ok as possible despite the awful news. It is a shock to the system, especially at an age where it feels like it shouldn't be happening at all, but life will eventually get better again. You just need to make sure to ask for help because even the strongest people out there struggle to do this on their own.
Sending love x