Colic happens. It does not require poor care and I have pretty much never heard anyone blame it on lack of training.
Lots of horses do not load into trailers. Even horses who are trained and have been doing it for eons can have a bad day and not load.
It sounds like you simply do not want to be friends with this person anymore and you are trying to make reasons to justify that.
Reasons are not required. Just let the friendship end.
Do not turn it into a long list of everything this person does wrong. It is far to easy to see the wrong in a person we do not want to like. Wrong that is not always there.