I never said you cannot get an STI when you're married. I'm just saying that I feel people are less likely to use protection during those times. I'm not saying they should or shouldn't, because I feel like you should always use protection unless you want to get pregnant and you can never trust someone 100%. People cheat and sometimes without us being aware of it (I'm sure some women or men know their spouses are in affairs), but you should always protect yourself. If someone decides to not use protection in their marriage or in a relationship, that's their decision.