I need help… I’m stuck and struggling

Almost 2 months on and I still struggle everyday.

Long story short, my fiancée was messaging her ex-boyfriend and had phone calls with him for just over 1 week.

I chose to stay. Each day I want to message him, the temptation is there. But what would I say? Should I message him? I still think about the whole situation each and every day.

Please help me.