what explains memory loss during important life events?

[voleguy]

While dating my wife prior to our engagement, we learned that I forgot the first time we were seriously intimate after only three months. Not just the event, but the whole evening. What we wore, where we went for dinner. I am a healthy person besides. I remember our first kiss, random story and movie plot lines, etc. After discussion, we also realized I have a hard time remembering first intercourse with other partners earlier partners. My wife remembers all the details. Therapists I've seen downplay it. Not everyone remembers everything the same way, they say. I feel cheated I don't get to share this memory with my wife.  Is this some kind of stress/anxiety related memory loss, or not even putting the memories down?  Even if all went well, and both of us were very happy?  Is it a common issue? Thanks.