Dear Sasha,
“I have been married to my husband for 15 years and we have had a good marriage so far. The last fews nights I notice, he steps out onto the balcony for a phone call around 9pm. This behaviour is unusual because he talks on speaker all the time in our bedroom. I know this is wrong on my part, but I checked his phone and the 9pm calls are with an office colleague (who I might add is a very pretty single girl who I have met at his office party). I have not been the one to read too much into such situations, but this nagging feeling that he could be engaging with an office romance is more than bothering me.
I feel uncertain about how to deal with this situation.”
Dear Friend, 
I understand that you are perturbed about this situation. The positive thing working for you is that you have had a good marriage for the last 15 years. For any relationship to work well, there has to be an element of trust and good communication involved.
So my advice would be very simple. Rather than snooping around and going through his phone records, set up some alone time with your husband and have a frank and honest conversation. Tell him that you feel unsettled for the last few days due to this incident. Patiently hear out his side of the story. Maybe there is nothing to it and you are reading too much into it or maybe not. There is only one way to find out. A conversation.
When we doubt our partner in any way, you can be sure, the relationship will spiral down. So ask and ask and ask more questions till all your doubts are settled. But once settled, let the matter rest in peace.
Good luck.
Much Love