These were written by a fella named David Wygant. I do not know who he is and I am too lazy to do an Internet search to find out. These six relationship breakers were written for "daters" but I figure they would apply to married couples as well.
1. Prying into private info. If you suspect your partner of betrayal, does that give you the right to start reading your partner's email? To listen to his/her voicemail messages? To hack into his/her online profile? The answer to all of these is "no!" You should never dig through your partner's personal emails or listen to your partner's voicemail messages. You should never dig through your partner's personal emails or listen to your partner's voicemail messages. By doing this, you violate not only your partner's trust, but also the trust your partner has with anyone who left those voice messages and emails.
2. Lying for the greater good. Lying is never good in a relationship, although we've probably all been guilty of doing it. Lying to your partner in an effort to avoid hurting him/her or to avoid confrontation may seem like a wise decision. Regrettably, you will end up digging a deeper hole for yourself when that lie is exposed, which is almost always inevitable. When caught in this situation, you end up hurting your partner anyway, and whatever you were trying to protect your partner from -- by lying to them -- will be even worse because of your deception. I recommend honestly communicating with your partner from the get-go.
3. Pulling a "James Bond." You should never snoop in your partner's private things (drawers, wallet, filing cabinet, or private records -- such as bank or credit card statements). Furthermore, nothing justifies snooping. No matter what you have a "hunch" about, snooping through your partner's things should never be pursued to confirm or deny your hunch. Your partner's possessions and personal records should be kept private unless he/she gives you permission to look at them. Spying on your partner is one of the most blatant violations of your partner's trust and will achieve nothing except having your partner never trust you to be alone near his/her things ever again.
4. Designating yourself "Magnum P.I." Another ill-advised way some people try to verify suspected bad behavior by their partner is to take on the role of private investigator by attempting to "catch their partner in the act" of doing something. Whether this takes the form of searching for your partner's car by driving by his/her house, work, or gym or it takes the form of following your partner in your car, this is something you should never do. Even if you have a convincing hunch that your partner is hiding something from you, stalking is the wrong way to address it. If your partner finds out you've been "tailing him/her" in your car, he/she will no longer trust you.
5. Sending others to do your dirty work. Don't ever send a friend or anyone else to gather information for you about your partner or to spy on your partner for you. This means, don't send a friend to go hang out where you know or suspect your partner will be. Don't have your friend try to eavesdrop on your partner's conversations in places he/she goes. Don't ask your friends to use their cell phone to snap covert pictures of your partner. All of these favors from friends not only violate your partner's trust, but also reveal your total lack of trust in your partner.
6. Checking up constantly. One of the biggest ways to reveal that you don't trust your partner is to manifest that distrust with paranoid and obsessive behavior. While calling your partner regularly is quite normal, calling him/her incessantly to "check up" comes off as obsessive and will drive your partner away. If, for example, your partner is unable to answer his/her phone for a few hours and by the time he/she accesses it he/she discovers you've called 50 times, you not only come off as being paranoid and obsessive, but you clearly communicate to your partner that you distrust him/her. Also, when you panic every time 10 minutes go by without a reply from your partner by a phone call or an email, it sends the exact same message.