Ok, first of all....I don't trust ANYONE 100% and that includes my husband of 14 years. Maybe that is a fault, maybe it is a defense mechinism, I don't know, you decide.
I don't believe my husband has EVER cheated on me but people are human, they make mistakes (and if he makes that mistake he will be drawing back a nub and I'm not talking about his hand either) and just because he is married to the most wonderful woman in the world (me!) doesn't mean he is not capable of doing something stupid! I trust nobody 100%.
I get my obgyn exam every year, they ask me if I want the tests, I say yes, what the hell, I'm there, I'm in the position, why not? May as well milk my insurance, after all I pay for it!
Especially with that new "disease" HPV out there that causes cervical cancer, I believe EVERY woman should get tested for STD, whether they are married or not. My friend who has been with her husband for 15 years, he cheated on her 3 years ago. She took him back (mistake #1) she recently went for a pap exam, it came back that she had to have a scope type test done for HPV. She was saying if she has it, it could be from when he cheated 3 years ago. She is still awaiting results. She could now have cervical cancer which will possibly kill her and in the very least impact her life in a huge way because he was an idiot. I researched it, she had a pap a little less than 3 years ago when he came back, she did not have it and gave birth to a child since then and did not have it. It is HIGHLY UNLIKELY that she contracted it from the time he cheated 3 years ago, it was probably due to the fact that he is still cheating which leads me to mistake #2.....the bastard is still alive!!!!!!!!! But ofcourse she does not believe that and I can't make her understand!
So yes, married, unmarried, gay, straight, singly, not sexually active, or old as dirt, everyone, especially women should be tested along with their regular pap.
This is the way I explain "trust" there are women who sleep next to a man for 20, 30 years and never even fathomed or realized the fact that the man the vowed to love, trust, and honor and vise versa had been molesting their child right down the hall. If things like that can happen, then anything can happen and thinking "it won't happen to me" is just stupid! Nothing wrong with trusting and in most cases it won't happen but it doesn't hurt to be cautious!