You see, this is why I always buy toothbrushes with different color ends. That way we never have this problem. It’s nice to be close, and when you’re kissing on a semi-regular basis, there isn’t the argument about germ spreading to be concerned about.
Generally, however, sticking to your own toothbrush is to be recommended. Forgetting whose water bottle is whose is probably a little less gross, although you could get different colored ones of those as well.