DESIRE to show her is an awesome first step.
Sorry, but recovering from infidelity does not take 18 months. Show me that person please, or give me that pill. Betrayals are betrayals.
I also want to say that understanding more about issues for survivors has helped me put his actions in context - and has helped me develop compassion for someone who was very hurt and carries those scars to this day. But understanding certainly didn't help me build trust in the beginning. It actually felt, for a long time, just the opposite.
When we discover an infidelity, we want to believe that we have control over keeping it from happening again. We don't freely admit it, but we believe that if we do the right things, say the right things, act the right way, there will be no more betrayal. When you first learn that this behavior has ABSOLUTELY NOTHING to do with you, it can actually hurt trust for a time period.
I don't mean ANYTHING negative against the survivors who come here to support us supporters - but there was a period for me when things felt very hopeless. And I have read, I've attended support groups, I've been on here for almost 2 years - and the more I did that, the more I understood my husband and the more I wanted to support him. THAT SAID, it also made me feel like there was NO GUARANTEE EVER that he would be able to fight these demons and there was NO PROMISE EVER that anything I did or said would save me from feeling this pain again. And yes, I know this is true for every human who walks this planet, it is just a little more true for people with addictions and for people with the most traumatic of scars.
That said, tell her you want her trust. And then do the good work, the difficult work, of building a human being worthy of trust.
I once read a very technical article about trust building and I think I shared it here a long time ago. This is the short form of it: http://www.beyondintractability.org/bi-essay/trust-building
For me, my trust these days has two levels. Can I trust your behavior (aka, do you do what you say you are doing to do, do you tell me the truth, do you communicate freely and openly) and then also something more like a foundation - is there a person in there who can back up all of the rest of it? Is there a person in there who understands himself and his needs and wants and desires and PROBLEMS enough to be able to speak the truth, his truth.