Unless it added up to way more than a few standard doses I don't think there's any harm. However, both drugs work via the same mechanism so I don't think you'd get any added benefits.
Hmm...the only time I ever experienced this was when the new girl was a downgrade in the looks/body department which doesn't seem to be the problem in your case. Are you still hung up badly on the ex? That is the only explanation I can think of if it's not due to being less attracted to her...
If you get hard as a rock beforehand...then the rest of it is probably mental/psychological. For a guy 40+ like myself though Viagra and other similar drugs to help turn back the clock.