In short, I've made a mistake of being overly friendly and supportive to another person and can't deal with the massive backfire due to me being untrustworthy. More details below.
I met my girlfriend, now wife, let's call her Alice, a few years ago in an online community. By that time I had had a close female internet friend, let's call her Diana. We used to talk often and a lot privately, as well as publicly on a social network. As Diana was kind of a chatterbox, she shared many minor things about her daily life, which I absolutely didn't hesitate to ask for or use as a basis for interaction. When she felt depressed or sad, I sometimes would cheer her up with a compliment. To add to that, we used to call each other various diminutives, or wish good night, or make virtual hugs. There was one time we exchanged real letters, very kind ones.
It's not too hard to see now that I have been digging my own grave, but back then I didn't feel like it. I had no intention of making our relationship with Diana romantic or attracting another person to me, all I wanted was to keep it a friendship, and I genuinely felt good acting so. To many people around, including Alice, my future girlfriend, what I and my friend were doing looked like blunt and open flirting, but I only found it out later.
After me and Alice started making out, I continued being friends with Diana and behaving this way. I was sincere, supportive and open with Alice, but at the same time I was pretty shy about her being mine, so I behaved more quietly and didn't act as open on public as I did with Diana.
A few months later, when me and Alice have finally met in real life, and a couple of months later, when she moved to my place, I noticed tension. She's been asking a lot about Diana and our interactions (as well as my relationships with other female friends, which were as well nothing but friendship) and turning less and less happy, thinking of herself as someone of "second sort". I tried to solace and condone her, and to explain the situation, all to no success.
Since then, it was a somewhat recurring topic in our relationship, where I've often been blamed for giving too much attention and support to Diana and — allegedly — admiring and loving her, and having only being making out with Alice in despair or because of rejection. Almost always there were long conflicts abd arguments afterwards, which still led to nothing but tears and disappointment for both sides.
Despite that, we were able to get along. It was the first time for each one of us, and when the topic of me behaving too warm with Diana wasn't brought up, we were happy and friendly with each other — until next time. I have never really sat down and done a side-to-side comparison of our private conversations and interactions to prove my points and explain what I felt, so that I could be more trusted. It was (and still is) especially hard due to me sometimes lying on different topics, or generally going easy about the promises I've made, which essentially made me a really hard to trust person. It's also worth adding that Alice has had, and still has, generally low self-esteem, which I failed to boost or help her with, and all my words on the topic of Diana are always met with suspicion that I want to twist the facts and Alice herself meant nothing to me.
Yet, we were able to sweep this under the rug with intermittent success for a few years, until recently Alice confronted me again. No arguments from my side are taken serious, no attempts to sit and talk it out are appreciated, as well as my efforts to re-visit the situation and provide an explanation for my actions, and I lost most of my hope of restoring the relationship when met with denial.
This brings me to a question: is it possible to restore Alice's good faith in that I wasn't flirting, considering the prejudice, and lack of trust, and her impression of being the second option? And if yes, how?