Does anyone have any experience/tips on investigating a workplace affair?

I found something very suspicious...
She has a coworker that I know she's close with. He moved here from another state with is wife about a 1.5 years ago. She called a cell phone from his old area code the very night she dropped the bomb. It was a 40 minute call shortly after she left the house. She had another 25 minute call to the same number a few days later when she was "out with a girlfriend."

I can call the number another time from a pay-as-you-go phone and see who answers to confirm it's him.

If there is in fact an affair there, the lack of frequent phone calls/texts is easy to explain since he is also married and wouldn't want his wife to find out.

I realize this could also be nothing, but the call the NIGHT of the bomb is very suspicious.


M34 W35
S5 S2
T10 M6
on/off over the years including her A
Recently-
Nov 2015 bomb
Nov 2015-Feb 2016 Reconciling
Feb bomb
March-April Reconciling
May - bomb
Mid-May I tell her I'm done