I'm so sorry you're going through this op.
Your first priority has to be your health, I'm sorry but in my experience (ex nurse but admittedly not sexual health though I suspect this is even more true there) men tend to not seek testing/treatment until they have symptoms and often not until those symptoms are really worrying them so I think your first priority HAS to be Sti testing and possibly even hiv pep as he had high risk exposure potentially
I'm sorry to add to your stress at this time but I couldn't in good conscience not advise you to do this.
In terms of the rest
I have been through similar as exh cheated.
If you're struggling to eat at the moment try nutritious drinks - soup, milk, fruit juice, smoothies
Take vitamin supplements
Do whatever works to help you sleep wherever that may be, I couldn't sleep in "our" bed for several weeks so I slept on the sofa, after first few days of resisting that reality I gave in and moved pillows and quilt downstairs so I was at least comfy.
Talk to somebody in real life - doesn't have to be friends/family although they would likely be supportive, but sometimes it can be easier to talk to an acquaintance or a professional (dr, counsellor, nurse, support worker)
Don't be too hard on yourself - if the housework or whatever slides for a bit fuck it! Do the min to keep things going if that's all you can cope with - that said of being busy helps that's ok too but don't overdo it
Finances - this is important though, collate all official papers and documents - certificates, bank statements, mortgage deeds etc IF you have a joint account please be aware that a very common tactic is to empty it before the wife can!
Get any money you get for you or dc is paid into an account that is solely yours ASAP - warning if you have an account with the same bank as the joint account, as soon as possible open a new sole account with a different bank - if he takes the joint account into overdraft the bank can repay the debt from your sole account if it's the same bank.
Get claim in with cms ASAP - because they only backdate to 1st date of claim, his still living there does not prevent this, the marriage is over you are separated but just living at same address - but you must not do anything for him like laundry etc
Get claims in with dwp if you're eligible, it doesn't sound like you would be necessarily but check on the online calculators
If I think of anything else I'll of course post