Your one statement really says it all for me, "Until you believe your mate understands your pain and that they grieve over what they’ve done to you it’s hard to trust."  It has been 5 years since discovery and things are good, maybe even in many areas better than ever, but I have never felt that he grieved for what he had done or realized the cost.  The operative word there being "felt" and feelings are not always fact.  However, trust is really slow coming for me because I haven't felt there was much regret.