Let’s be honest, a lot of people don’t have “trust issues”. They have “I’ve seen this pattern of behavior before, and I’m not about to go through the same crap again” issues.
It’s called Wisdom. Wisdom recognizes patterns.
Yet what wisdom often forgets to do is ask itself why is it experiencing the same pattern again. Lots of times the issues you experience through others are a reflection of unhealed, unconscious patterns in your own life.
Ask what you did to attract such a person. The people you attract are spiritual lessons and blessings. So don’t be so quick to look at them as darkness. Look at them as reflections of your own darkness.
However there are limits to this. Beauty attracts both flies and honey, and so does the light.
Also no, it’s not up to you to fix anyone, but sometimes if you tell someone their patterns are unhealthy, you can get them on the road to recovery. Many people pass up on great people over minor issues that can easily be fixed.
No matter what you will have to help your mate heal. No one is going to be absolutely perfect.