Personal Letter to my Italian Husband

I have a letter I wish to send to my husband before his return to england. we have been seperated for quite some time in which their has been another women. The other women lives in England. I am happy to try again with him only I need address this other women and make it clear that I will not tolerate any other person in this relationship if our marriage is to work.
I will share some personal stuff with you on the phone.
I just need help with putting this letter together. I feel it would be better to put it across in italian as he is italian. It may be I end up speaking to him on the phone instead.
I speak Italian only my italian is not great. He is an Italian native that has been living here for 15 years.
I need somone who understands my predicament and can help with positive language that comes across in a firm but loving way.