I Must admit i know what you mean! im only 6.5'' or is it 6.5' i cant remember the whole ' thing! anyway i digress! Dude its quite offputting when your pumping away and all of a sudden you think is she wishing it was her ex's or as big as his? ive had similar situ's and it hard but all you gotta do is say "Shes with me for my personality the other guy must be a bigger dick outside of the bed aswell" (Unless its a good mate) and smile to yourself knowing your the better Person!

Ciao for now!