Women are highly social creatures who often have a mix of female and male friends. This should not bother you. There is nothing wrong with someone having friends. However, if you find that she seems a bit more interested in one particular friend - especially if they are male - than the others, it may be appropriate to become a bit concerned over the issue.
She may start to talk about this friend more than the rest. She may show a lot of interest in this person. If she starts to compare you to this friend be on high alert.
It's a subtle, but very loud sign.
Her heightened level of interest may not stem from an actual affair that is occurring, but it could be from an infatuation or other types of feelings she is developing for that person.
This is the step that takes place prior to cheating.
The next sign is that she starts to display a lack of interest in you in general.
I always tell my clients that this is the final phase.
Most married women show a fair amount of interest in the men that they are married to. If you start to find that your wife does not show this interest, it could be that she has discovered someone else to show interest in.
In many instances, the cheating has yet to occur and you can actually put a stop to it and save the relationship before you lose it.
The best solution is a combination of 3 things: "knowing the signs that your wife may be cheating", understanding her needs and figuring out if you're making any seduction mistakes.