I think your issues here are not about ADHD; they are about trust.
Someone with a diagnosis of ADHD is not just an ‘ADHD Person’. The can (and will) present with other conditions or disorders that may also be complicating or even worse. I would say that depression and substance abuse are the main ones, but you can also have bi-polar depression and personality disorders too. People who have low self-esteem may be also looking for situations where they can get some validation of themselves, narcissistic people are always looking for people to find them attractive and worthy of love, sociopathic people have both poor impulse control and no feelings of remorse, the list goes on.
I would not just take out one known and consider it the only factor involved. Maybe the slip-ups here are a way for you both to accept that there is a clear issue around communication and trust and confront that. I hope this does not sound to judgemental or harsh.