My fiancé of over 3 years constantly says... "remember when we did "such and such"......and I will say......."It WASN'T with me"....

I constantly confuses, forgets? Who he did what with. In the first year - maybe - I could be a little more tolerable - but after this long?

Does he still harbour feelings for his ex? I am a carbon replacement? Am I that "unremarkable" that I blend in? Is he just insensitive, truly forgetful, or a combination of both?

It sounds like he may still have fond memories of his ex. Do you know if their breakup was a bad one.He may have not ever gotten over her.

It means nothing... It used to happen to me... It just means it was so long ago and sometimes you can't remember who it was with. But I think it's good at least he thinks it was with you. You should let him believe that. Obviously his ex wasn't so remarkable because he thinks everything is with you... Shows how good you are! Aww, he's in love... so cute... Be happy! We wish we had what you have!! Embrace him and love him as much as you can!

Well, one thing is sure ; he remembers things too well for his own good! I'd tell him that anything that was said or happened more than 6 months ago is off limits and no longer applies! If that doesn't do the trick then I'd seriously rethink your relationship with this guy. I wonder if your fiancé is related to my wife lol!

He's reminiscing out loud.

It's strange, but maybe he implies he would like to do that* with you. So, why not make a good memory?

*what he's saying