What is a relationship deal breaker for you?
If I cannot trust who ever is in the relationship with me, I will always have a negative feeling that I may one day be badly surprised by something this person has done.
This is true for me for all types of relationships.
If I cannot trust the person in the relationship with me, I will just not be able to feel comfortable with them. I wont be able to comfortably share things with them, talking to them, and being with them.