I have never known this to be true, but that said, who really knows. I have been with my fiance for 8 years now and he doesn't have lyme. Prior to this I was with someone during my worst part of this illness. We were together for 6 years and he doesn't have lyme either. From what I was told when I was going through it, was that sometimes couples end up both with lyme because they tend to do things together and go to the same places and could both get lyme for this reason. I never had a tick bite or rash so I will never know where or when I got lyme and I think that is part of the reason why some of us try to figure out how and why, but I don't think a lot of us will ever really know.
It is always best to be on the safe side anyway, but I know for me, it isn't something I worry about happening.