How do I tell my partner I think he has ADD?

I am on a 1 week break from my partner because of his odd behaviour. I told him he is chaos and I need to remove myself from the mix so that he can sort himself out, and that he is draining me of all my spirit and will to live.  During this week one of my male friends who has an ADD son emailed me asking whether my partner had got Adult ADD.  I looked it up on the internet and I have been crying for the last 3 days.  My partner has so many traits its not funny. I've told my partner in the past it feels like I'm dating a 15 year old and Im his parent/big sister/boyfriend all rolled into one.  He's actually a 31 year old male and Im a 40 year old female, so I thought maybe it was the age gap but I think not now.  He makes me laugh and he is very interesting and has a focused professionally mathematical technical mind and I love him and I still fancy him very much.  So the following is not a rant, its real stuff I have to deal with and I don't know whether I should tell him we need to discuss getting him tested or I should just end the relationship for my sanity.

At the beginning of our relationship he had bad sleep issues where he would terrorise me by shaking me awake and just stare at me, sing or have long conversations with me. Next morning he would not remember anything.  I told him to quit caffeine and things got better and now he only talks in his sleep every night which wakes me up.  I found it strange that he has no memory of his adult life but can recall detail of when he was under 12years old.  He cant remember what he did last week, and he has forgotten whole years of his life.  I thought he was deliberately being secretive.  He cant sit still, I tell him to stop foot tapping when he sits on the sofa because it makes me feel sea sick.  He is the messiest man I have ever met in my life, he leaves his clothes underpants and socks on the floor and will leave them there...I wondered why I was ending up doing his laundry and he wasnt even living with me!!! In the end I asked him to use my laundry basket if he didn't want to take it home with him but he cant even do that.  He talks over me all the time...he will ask me a question then while im answering he'll carry on talking!  When we're with friends (his friends as well) in a discussion over dinner or anywhere he will lose the thread and I will have to explain everything again.  I've found that he cant really articulate himself sometimes but that's ok, its the times when he talks so fast its like hes talking a foreign language, that frustrates me.  When we're out with friends he either falls asleep at the dinner table or goes AWOL. He doesnt know his limit and half the photos are of him passed out, or he will disappear from the venue to go and get packet food (its ok hes not overweight) and on one occasion he then got lost. Everyone went home and I was left with a friend trying to direct him back to the venue over the phone. Anyone would think he was a 15 year old doing drugs (which he certainly does not). I don't mind helping him in other areas - like paperwork and admin type stuff, or updating his resume etc. Its the every day clumsy chaos that is driving me insane.  He also has such low self esteem which he hides and 3 months ago he put himself on herbal anti-depressants (St John's Wart) and got himself an S.A.D light. He will have moody days but deny anything is wrong then the next day he will admit that he was feeling down and apologise for his behaviour. Bless him, I dont know whether Im coming or going with him, so the Lord only knows what he's going through.  I articulate and communicate calmly with him but he finds it very difficult. He also has repetitive ticks but he's good at stopping when I tell him to.

At one stage he moved in with me but after two months of mess, chaos, braking things and him constantly saying "its only a glass, its only a marble work top...Its only a..." "I dont like cleaning Im better at cooking so you do all the cleaning" "Its just the way I am, just accept it", I asked him to move back to his flat that he was renting out to a friend and that we'd try again after refurbishing my flat.

I want to marry him, because of his qualities and he would make a fantastic fun outdoorsy father but Im scared I will be looking after two kids and he wont grow out of it. 

His 28yr old sister has odd phobias - will only drive on single lane roads (their retired dad will drive her to parties, shops and airports) and she has sleep walking issues, and has memory problems and refuses to use a computer.  His two cousins on his mother's side - one is 24yrs old, profoundly autistic and needs 24hr nursing as he cant even dress himself, and the sister is 20yrs and has just been put on permanent medication for OCD which was manifesting itself in violent outbursts. I once asked my partner's mother if he had been hyperactive as a child and she said "ooohhh!!! whatever made you think that??!"  I felt guilty I asked. But then he recently told me he was very disruptive at school and didnt get on at all and 'they' wanted him to 'get tested' but he refused because he 'didnt want to be labeled'. So when he failed his exams his parents paid to send him to a special school for 15 to 19 yr olds who dont get on in mainstream learning. I feel annoyed with his mom that she wasnt honest with me.

My partner fell backwards down a flight of stairs (drunk) 9 months before we met and was in hospital for 2 weeks with a bruised brain.  The fall also damaged the nerves connected to sense of smell.  He has no sense of smell now and with that he loads his food with salt and chillies to replace the lack of flavour we have through smell.  Ive told him all the salt will lead to heart disease and he should go back to the hospital to discuss his condition, but he refuses to ever see a doctor about anything.  He said that because of his profession he wont be allowed to do his job if he has on record any type of medical condition. This is true to a certain degree and will restrict him from a Health & Safety perspective. But if anything happened and he has not disclosed any medical condition he is potentially putting other lives at risk with the type of work he does.

Im worried that if my partner agrees to treatment to save our relationship, he will revert to type within a year and by that time I will be getting too old to have a first child. And will that child have similar issues? But the way he is now, I wouldnt trust him to look after a baby.

I dont know what to do.  Im seeing him in 2 days to discuss our relationship and where its heading but dont know how to tactfully tell him I think he has ADD and he should be tested. Or do I walk away before we get married.