I don't think either he or his daughter have behaved well in the circumstances but I have more sympathy for him.
From everything she posted about him and said about him in the years before the wedding, he was a good dad and they had a great, very close relationship (if you believe her and don't question her motives for posting all the stuff she did). He also spent a lot of his money on her education, travel and helping her to further her career.
I think she was embarrassed by him once she met Harry- he didn't fit. Lived in birder town in Mexico where he'd moved because it was cheaper, lived a quiet, downmarket lifestyle, watching tv in his flat walking to local store for food. Obese, badly dressed. She NEVER took Harry to meet him. There was no way he was ever going to that wedding and I think he was getting very stressed and panicky. Press around his flat fir months so he went out even less.
The photos were such a stupid thing to do and the explosion in the Press tipped it all over the edge. I was not convinced he really had a heart attack at the time- although I am now since the hospital confirmed it. It gave them both a way out.
I think her completely cutting him off is horrible and he has every right to speak up. Why should he not say anything? She has a mega PR and legal team to protect her. He has nothing. I think her behaviour is graceless.
The half-siblings don't help but they do at least seem to look after and maintain contact with their dad.
It's what happens when a member of the Royal Family marries an American with a lot of baggage. I don't like her, have not liked her since the relationship became public- I wouldn't trust her an inch, I think she is all about her and publicity, including during her charity work. Could it have worked if she and her siblings had been prepared to 'conform' and keep quiet? Possibly but that was never going to happen- the siblings are not that kind of family (unlike the Middletons who learned very quickly how to behave and what the benefits were of doing the right thing.) She is not that kind of person- visiting the site if the school massacre in Texas with a photographer and two huge security guards, not disguising herself at all, posing for photos at the memorial which were released and then saying it was a private visit and she'd wanted no publicity, exemplifies that.
But overwhelmingly, if she was telling the truth and he was such a great dad and she loved him so much:
Why didn't she visit him before or after she was engaged and take Harry to meet him?
Why didn't she visit him after his heart attack?
Why did she write him that unpleasant letter- and then tell all her friends about it, who leaked it's existence and content months before Thomas Markle spoke about it?
Why hasn't she visited him now?
I have more sympathy for him but him taking to YouTube and Lady Colin Campbell is not helping the situation. There is no hope for the relationship.
I think it is interesting that he and Dora Raglan still meet at her house, have lunch, he takes her flowers. They obviously get on still.