At least 20 percent of Americans have cheated on their spouse — that's a whopping one out of every five people. The crazy thing is that people don't enter a marriage expecting to be unfaithful, so once it happens, most people are shocked that it did.

Infidelity can creep up on you, but these eight things will help guard your marriage from it.

1. Realize you're not immune

The first thing you need to do when trying to affair-proof your marriage is realize that it can happen to anyone, including you. Being aware of this possibility allows you to safeguard against infidelity.

2. Avoid exes

What can start out as some innocent texting can escalate to a rekindled flame in no time. If you choose to continue a relationship with someone you dated, make sure you include your spouse. Meet as a group and never discuss something personal with your ex when your spouse isn't there.

3. Don't talk negatively about your spouse

Venting about everything your spouse does just creates feelings of resentment in your relationship, which will affect how each of you feel about each other. Instead, speak directly (but kindly) to your spouse about these issues. Open communication will help you resolve your problems, and strengthens your commitment to each other.

4. Don't withhold sex

Make sure that you and your spouse are having sex regularly. There may be times when you don't feel like getting intimate for a variety of reasons, but don't let this happen regularly. Let sex be something that you look forward to sharing with your spouse.

5. Don't put anyone before your spouse (including your kids)

Your spouse should be your top priority. Allowing other people to knock your spouse out of the No. 1 spot is not healthy for your relationship. Make sure he or she knows that they are the most important person in your life.

6. Don't watch porn

Aside from the fact that many people define porn as a form of cheating, studies actually show that people who watch sexually explicit material are more likely to cheat. Pornography makes people feel like they have more options outside the relationship and alights your reproductive instinct, making you more likely to cheat on your partner than people who don't watch pornography.

7. Fulfill each other's needs

You both have individual needs. Make sure you understand what your partner needs and do everything you can to make sure those needs are fulfilled.

8. Keep dating

You're growing as a person, and that person isn't going to want the same relationship she had 10 years ago. Make sure your relationship keeps growing as well. Keep thinking of new ways to romance each other and spend time together talking and building your relationship.