What Is My Wife Doing ? Is She Cheating?

Please some weeks ago, I got to know that her colleague (a male) calls her often. I told her but immediately she flair up and went to work with anger, she told me that the boy was calling him for work meanwhile they will see for sure the second workday, when you left home angrily without even fighting her.

The boy sent me some messages on WhatsApp explaining that she wants to collect a phone from my wife blahblahblah, I never replied the text, the boy called me twice on the second day and I didn’t pick, my wife told me that the boy saw her face look angry and that’s why he asked what was wrong with her and she explained to him, she told me that was why he was texting me.

Yesterday, I found out that the same boy still calls my wife and my wife calls him too, when I raised the issue again she flair up telling me the boy was calling him to ask her welfare.
What is confusing is that the first time they talk different things, why would a reasonable guy continues calling her after he knew it caused fight the first time, why would she continue too when she knows that it’s threatening her marriage.

My wife has been denying me sex for 3 months, tell me if that’s possible for a girl who loves to Bleep.

My wife has a child for me and she has been supportive financially, she does house chores everything, but she had betrayed me twice before, one was cheating, the other she stole money coniving with my cousins at my former business.

Please somebody advise me on what to do.