The Nine did an evil thing to the SSPX back in 1983. They tried to take the whole SSPX away from the Archbishop and the faithful Catholics who were looking to him for leadership.
What has their sedevacantism done for the Church, from 1983 to the present day? Don't talk to me about their general Trad apostolate, because they could have done that as an SSPX, independent, or other non-sedevacantist Trad priest. The Tridentine Mass, traditional sacraments, the Rosary, all the Trad devotions, chant, you name it. That's a whole different story. The Trad movement in general is important, useful, and critical for the salvation of souls today. Sedevacantism is not. It adds nothing practically speaking. It solves nothing.
I don't know if I'd go so far as to say "I'll never forgive them"... but let's just say I'll always remember what they did to the saintly Archbishop. They were his enemies on earth. Hopefully they repent/repented before death -- but they did an evil thing.
And who did they attack? The GOOD SSPX, the chosen vessel of election for the preservation of Tradition. The SSPX fell in 2012, but that doesn't mean it was always rotten. The Catholic Church "fell" in the 1960's. Was it rotten from the beginning? Of course not!
Nevertheless, I hope only the best for the soul of Bishop Kelly.