I understand completely FS. Our ES's wife's change toward us was "so sudden and so extreme". I always thought I was a pretty good judge of character and in that regard, like you I was "left feeling that it is very hard to trust anyone at all".
I also wondered if I could ever trust our ES again, and as time has gone on I've come to realise that no, I'll never be able too.
For me, time has helped reduce my sense of vulnerability on a daily basis but there are times when it hits me with full force and even now, if I'm anxious usually about something in particular, I don't like to leave the house.
Friends were very kind when Mr. S. was in hospital, inviting me for meals so I wouldn't be on my own, but I just wanted to stay here where I feel safe.