Hi Jay,
First, I hope you aren't tackling these questions yourself, that you haven't faced something in your life that makes you need to answer this question. I believe that trust really depends on the relationship. Trust between friends is different and a little easier to overcome sometimes than a significant other. If a friend hurts you by saying something or doing something that makes you feel bad, that's much easier to overcome than if a SO does it. I personally think that trust can be overcome in a relationship with a SO but I don't believe the relationship will ever, ever be the same. I could never cheat on anyone, I'd sooner drive a stake through my heart than do that. If someone did that to me, the relationship would be over.
Transition is interesting because I think that many times we fault out mates for straying, for finding love somewhere else. I think they should communicate their unhappiness before cheating (emotional or physical) ever really begins. I believe that a SO relationship can go from marriage/really serious to just friends with mutual agreement and can be stronger than ever before. I believe that you can go from spouse/SO to just really, really good friends and both parties can be much better off than before. I think too many people hold on to SO for dear life when sometimes the best thing to do is let go of the marriage. I'm not saying let go of the friendship, of the bond, I'm saying let the other person be free to find their happiness if that's what they truly want. Transitioning is selfish in an of itself but to try to force a relationship is really tough. Ok, I went way out on a tangent and I apologize for that. I hope you are doing ok and not struggling with heavy matters in a relationship. Meghan