6. They constantly need "privacy"
Similar to needing more alone time, if your partner suddenly becomes increasingly private, especially about things they used to be open about, it could be an indication of infidelity. Some measure of privacy is important in a healthy relationship, but an abrupt 180 in the level of openness the two of you once shared can be a cause for concern.
New internet passwords, hiding cell phone or credit card bills, utilizing locks more frequently — all these are highly suspect behaviors that often point to an affair. Unfortunately, if you attempt to uncover the truth as to why your significant other is doing these things, whether openly or surreptitiously, it is often met with anger and defensiveness. Your partner’s opposition to your questioning may also be a red flag.
Every couple needs breathing room, so a little privacy is okay, even important. However, excessive secrecy should be investigated, especially if it occurs suddenly.