now, if you really think that your spouse is cheating on you. directly ask. there is totally nothing wrong with asking your partner what you are thinking. this will tell your partner that you are thinking about this since you feel that it is really happening. now if he is a good partner, he or she will improve the ways in keeping the marriage. and if you really want to hire one go ahead. what if your partner is not really cheating. so this might destroy something, like your marriage. trust needs to be taken care of upon the pillars of marriage. if you don’t trust your partner, tell him/her that your trust is fading due to the things that made you conclude that he/she is cheating.
this is actually a problem, if you are a good partner, you don’t need to solve a problem with something that might also become a problem. do not ever think of revenge if things get serious. this will not help. this will just add more problem.

now if again you really think your spouse is cheating, tell him/her straight. and tell your spouse you want to have a happy marriage, and the things your partner is doing is making you think that he/she is cheating. and there is no marriage that can survive with a cheating partner. and if he/she does not succumb, you will be forced to get a divorce.

i know i did not answer your question, just want to tell you whats in my mind.