Ordinarily I'd get, and expect my partners to get, tested every year. (My husband agreed to hold himself and his partners to the same standard, and one of them ended up finding she was positive for a high risk HPV strain because of this). I'd get tested once a year period during non-monogamous times, regardless of if any NEW partners were added on any side.
However we found out last year my husband is HSV2 positive (he just got that test added as it's not a normal test, and he's thinking he got it in the mid 90's from somebody who let him know after the fact she had it) so I am getting tested every 6 months, since I don't have it after 7 years, and my boyfriend doesn't want it, and if I get it it'd end our ability to have intercourse. If we broke up and new partners didn't feel so strongly about it, I'd go back to 1x a year.
There are no guarantees for HPV since it there's no test for men, so all you can do it decide where your risk boundaries lie, and what your barrier requirements are (and it doesn't hurt to get screened every 6 months for oral cancer by your dentist). HSV2 doesn't necessarily show up for up to a few months, so recent tests aren't 100% against that. Condoms for vaginal/anal/oral sex pretty much cover all STI's except for those (well except that new strain of drug resistant strain of gonorrhea?) So barriers for everything is what we do with new partners at least, so we don't have to sit around worrying so much.
At some point when a situation seems long term and stable, barrier changes can be discussed with all relevant partners at that point. For us specifically though, that point wouldn't ever come with somebody who had regular new/casual partners for us, there would always be barriered oral/etc sex with them just to minimize stress and risk, so we didn't have to deal with OSO's metamours sticking to our level of testing.
Happiness will never come to those who fail to appreciate what they already have.
Last edited by Anneintherain; 07-02-2012 at 07:58 AM.