Not been in a relationship, but my best friend (m59) was diagnosed around 20 years ago, after me pushing him to get a diagnosis for the whole time I had known him.
At 59 he has had 10s of relationships, but the longest one being 4 months.
His desperate need and desire to be in a long term relationship was the reason I encouraged him to get a diagnosis and help.
He got the diagnosis but refused therapy or medication, insisting there was nothing wrong with him, it was all the fault of the women who he dated that the relationship failed.
He is a dear friend to me, and we share a lot of interests and hobbies.
However he is:
Fixated on routine while the latest 'routine' lasts.
Obsessed with his hobbies.
Talks constantly without listening.
Struggles to follow simple instructions.
Needs everything written down.
Is rude to staff in shops and restaurants, and can only see he has been when I point it out.
Is obsessed with conspiracies. Rarely is anything said/ done to him by anyone that he doesnt believe has an alternative motive.
Is overly sexual, creepy and stalky with a new love interest.
Misunderstands humour/sarcasm/wit.
Is terrible managing money.
Struggles with basic hygiene and housework.
Seriously believes he is superior to most people.
Is a terrible hypochondriac and talks endlessly about his health or lack of it.
Makes plans to do so many things, but in reality does nothing.
Has rigid views on things and will not be swayed.
He is exhausting.
Past partners have commented that he's a narcissist ( I don't know very much about that so cannot comment)
That he's totally irrational (he is)
That he has meltdowns that they cannot make sense of (true, but I help him with those)
Aside from the above he's kind, honest, loyal and reliable. But definitely not relationship material.