You're exactly right in your interpretation of the other discussions. STDs are not just infections that happen to mostly involve the genitals; they are sexually transmitted because they require the intimate contact of sex to be passed from one person to another. Many people sort of assume that "just one virus" is enough for an infection to pass, but that's the case with almost no human infections; varying levels of exposure are required. For the STDs, heavy exposures are necessary, and/or the causative bacteria and viruses must have access to particular cells and tissues that are internal and not readily exposed. And STD bacteria and viruses are not present on nipples or anywhere else on the skin; and even if they were, touching them (or oral contact, e.g. mouth-nipple) is no risk. Neither is kissing anywhere on the body, even with kissing vigorous enough to leave a hickey or bruise.

The bottom line is that indeed you are "more worried about this than [you] should be". These events were no more risky than shaking hands with someone. Such contact risks colds, influenza, etc -- which are among the easily transmitted human infections. But not nearly close enough for STD/HIV risk. Don't worry about it!

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD