This happened to my wife and I...but in sorta reverse, unfortunately, lol.
I was with her first in college (I'm average, not small), but when we broke up for a bit she started sleeping with a guy friend of hers who turned out to be very large (around 8 inches as compared to a toy of hers).
He had had a crush on her for a while and liked that he had kinda taken her from me, and he wanted to know if he was bigger than me, which she admitted he was.
A month and a half later we were back together after they had broken up, but they were (and are) still friends, which made things a little awkward and embarrassing when she eventually told me about how large he was and that she had told him (not knowing we were going to get back together, obviously) that he was alot bigger than me.
Eventually I got over the jealousy aspect of it and just became more fascinated and turned on by it and hearing about things he had done with her, especially since we would still be hanging around and going out with him in groups, and talking about him still turned her on.
It would've been more embarrassing though had he known (or found out now) that we got a sex toy for her in his size as a result of it turning both of us on, lol.