When jealousy shows his 'ugly head' and becomes a problem in your marriage or relationship, we often assume that it's the jealous person at fault. It may be the case sometimes, but not always. And, surprisingly, it has often nothing to do with cheating!

One person often feels jealousy for 'hidden' reasons which need to be addressed within the relationship. These often are: 

1 - That person is actually neglected within the relationship. He/she is facing daily indifference or daily apathy from his/her partner or spouse.  Jealousy here signifies nothing to do with cheating but all to do with wanting to be appreciated and noticed by one's partner or spouse. So, if the couple learns to reconnect (through therapy, for example), jealousy will simply dissipate! 

2 - That person is abused (emotionally or otherwise) even to a 'small' degree, whereby she/he faces constant 'put-downs' from the partner/spouse.  Jealousy here - once again - has nothing to do with cheating but all to do with the need to be nurtured, supported and cherished, which does not occur in the relationship (but instead quite the opposite is taking place). In this case therapy is necessary, because such a negative situation is highly detrimental to both individuals. 

3 - That person suffers from low self-esteem despite being in a healthy relationship, but this creates a constant comparison with others and therefore jealousy sets in. Again, this feeling has nothing to do with actual cheating. 

4 - That person is justified in feeling cheated because of unreasonable 'flirting' between the partner/spouse and others (to say the least). In this case, of course, therapy is also necessary to address the common reasons why one partner carries out flirting behaviour outside the relationship or marriage (or even cheats). 

So, in summary, jealousy is often really useful in that it highlights deeper problems which absolutely need to be addressed. Simply telling oneself that we are wrong when experiencing jealous feelings and trying to repress them is absolutely wrong to both parties.  Jealousy a symptom, it's not the cause of underlying issues that need to be resolved. So, like all symptoms, the best cure is not repressing it but rather understanding the real cause of it.