Hello Pollywobble,
Gosh, that's a difficult situation for you to deal with. I'm glad that you already have a mental health referral in place to assist. Do you also have support for yourself and your own well-being? If not, it might be worth getting that in train, pronto, by speaking to your GP. You need to be OK to give your husband the support he'll need.
The Memory Clinic appointment should not be something to be worried about. The idea of it is that the medical professionals get an idea of your husband's situation with a view to providing the help and support he needs, depending on the diagnosis. The format may differ depending on where you are in the country, but the aims will be roughly similar.
On that basis, it is likely to entail a initial chat covering the history of your husband's general health, and a discussion of the difficulties he (and/or you) have noticed that he's been having. Do be as honest about these as possible, there's no shame at all in struggling with day-to-day tasks.
They will likely want to do some form of memory assessment, either the ACE III test - for what this looks like, search 'ACE III' or 'Addenbrooke's Cognitive Examination' with Google - or a mini version of this, just to get an idea of where your husband is right now and identify the type of difficulties he is having.
They may suggest something like having a scan (e.g. MRI or CT) to aid them in a more firm diagnosis, but not always.
They may discuss medication which could help, although for us this came on a follow-up appointment.
The idea is that by having this appointment they can start to look at the best way to support him, and also you, to live as well as possible with whatever the diagnosis is. That's what it's about really, living with it and making the most of life, not letting it wreck your life. Sounds easy, it isn't always but you won't be alone.
The Memory team should be able to point you to more information to help you - if they don't, the the Alzheimer's Society website is brilliant, and if you have questions (I had loads!) then use the Dementia Support Line - 0333 150 3456
or ask the folk here, since they have a wealth of knowledge.
All the best, SeaGirl