Are you curious if your spouse, or significant other, is cheating on you? Cheating happens more often than you think. Here are some steps to find out if there is cheating going on.
First you need to think about what you consider cheating. Some people are perfectly okay with their spouses looking at porn, going to strip clubs, or going out to eat with other people. Decide what YOU consider to be cheating and go with that. Preferably, sometime during your marriage, you should have both talked about what each of you considers to be cheating. That way, you know where you stand. You can't very well tell your wife you are perfectly okay with her looking at other men on the computer and then accuse her of cheating, or vice versa. You need to have established your boundaries.
Does your spouse have a MySpace, Facebook, or other social networking account? If so, this is where I would start. You should look over his/her profile to see if anything looks out of the ordinary. Check for signs of cheating. View the comments and friends. If he/she has given you the password and told you that you may get on it, then (and only then) would I resort to logging on the account. Once in, view the messages (sent and received) and also view friend requests and DON'T forget to check the pending friend requests. Also, try searching for your spouse on these sites. If they don't have an account (that you know of) they might have made one. And if they already have an account, they may have a separate account that you might not know about.
Email. If your spouse has given you the password information and given you permission to get on it, then I would check here next. I know that sometimes when you think someone is cheating you want to hack into all of their things. You STILL need to be respectful of their privacy. Plus it is illegal to do some snooping, and you do not want to get in trouble. Check the email inbox, sent, AND trash. Some email accounts automatically delete the trash box. Some don't. So, sometimes someone will delete an email and really it just goes right to the trash box, waiting to be emptied. Check the contacts to see if there is someone there who shouldn't be, that you know of, or someone you suspect your spouse may be cheating with.
My next step would be to go to Google or Yahoo and enter his/her email address in the search bar in quotations. For example: "JohnDoe81@yahoo.com" and hit search. This should bring up every time the email address was posted somewhere online. I would do the same searching for your spouse's name. For example "John Doe" and that will bring up all of the results for his/her exact name. You might also want to narrow it down and type in the name IN quotations and then beside of that your city/state OUT of quotations ("John Doe" San Francisco). THEN I would search for handles that he/she uses online. So if most of the places your spouse signs up for asks for a screen name, and you KNOW he always uses JohnDoe81 as his screen name, type that into the Google or Yahoo search box IN quotations.
Check the online dating sites for your spouse. Check all of them that you can find. Check Adult Friend Finder.com too. Actually this is quite fun anyway because you can sometimes find people that you know on these sites. Some might even be cheating on THEIR spouse!
Cell Phone. I wouldn't necessarily snoop through his/her phone unless they give you permission. If they DO give you permission, look through the recent calls, texts, and check out the pictures/videos/sounds too. This might tell you if there is cheating going on. If you can't look on their phone, you should be able to view your billing statement which will have the calls logged in there. Check out the bill for any suspicious numbers. If you need to, use Whitepages.com reverse lookup to trace the numbers you are unsure of. If no results pop up, it's probably a cell phone number. Try calling that number from a pay phone.
Check credit card/banking statements. Look for hotel visits or restaurant receipts. If you see a charge from McDonald's for $5.00, I really wouldn't worry about it, but if you see some fancy French restaurant up there that YOU didn't go to with your spouse, I would worry unless it was a business meal.
Follow your spouse. This would probably be my last resort. Follow them when they go out to see where they are going. You may be surprised.
If all else fails, you may want to hire a private investigator. It can be costly, but if you really feel your spouse is cheating, then this may be the way to go.