When do we stop deserving others trust?

When I first found out that Drake had slept with our friend...my "friend"...Onika, I guess I felt more betrayed than anything. I wasn't really angry... I mean I couldn't be... We weren't together when he slept with her, even if it was only days after our break up, he was single. But I guess it was more of the fact that it was HER and that she -a friend- had decided that it was okay to fuck the love of my life for the last 5 years.... I was feeling betrayed as a friend and sorta going through this life lesson that: not everyone has the same respect and boundaries for friendship. What some may consider " showing loyalty, respect, and honesty towards one another as sort of a silent contract between 2 people/2 friends..." Is different and varies between each person.... And I was learning that there were a few lines of fine print in both Onika's and now Rachel's...a fine print I should've been made aware of... One stating it was ok to sleep with another's LONG TIME LOVE after a horribly hard break up, immediately afterwards.....the feeling of that emotional knife in your back is a confusing one. Why is it there? Should I be feeling like this or am I just overreacting? Will it ever get pulled out...even a little?  Turns out you can't trust manyeople to have morals...or boundaries...respect. It's all humanity has....but we don't even have that.