This sounds like a similar story to my son. He failed modules at the first year, retook them and passed some of them, then failed everything at the end of the first semester of his second year. At this point he was looking at doing a full second semester with 3 retakes.
He is at Uni in the same city as us so we are on hand to help him. He exhibits many signs of ADHD and an ed psych report confirmed learnng difficulties but also very high abilities in things like verbal reasoning.
He was failing modules because he was not doing coursework assignments due to an inability to organize himself. He was OK with straightforward exams because he's not unintelligent.
So we went to the learning support department of the university with him to work out what to do. They have been very good. They see this sort of thing all the time and they will talk to tutors and know what can and can't be arranged. He was allowed to drop a module in the second semester and with me helping him keep track of deadlines and coursework requirements, he managed to pass the retakes and all the modules in the second semester.
It's been bloody hard work for all of us. He will have to do the 3 modules he has failed or dropped in an extra year. He will probably only get a 3rd and will have a tonne of debt. However I think the achievement of getting a degree will do wonders for his self confidence.
Given his A Levels, he was never going to get on conventional graduate schemes but I'm sure he will find a niche.
We gave him the option, almost encouraged him to give it up but he wanted to keep going.
My advice would be to get involved, find out exactly why he's failing, see what options (learning support department, reducing workload) are available.
People will tell you he should be standing on his own feet and you should let him find his own way. These people don't understand ADHD. If he does have ADHD, he will not do it for himself. Hopefully you will find a way.
It would be really useful to do some research into ADHD with him so that he can realize it isn't all about over-excitable schoolchildren. it manifests in many different, frustrating ways.
One other thing, you may find his disenchantment with the subject comes from failing the modules. If he can experience some small successes the enthusiasm may come back enough to get through it.
I hope this helps