We commensurate with you, about your Life you have led this far, which as you have described was a living hell. Twenty years is a long time to live in such hell.
So, what are your options:
Divorce, which you are actively considering could be one of them. Remember, you have 3 adorable children, who for no fault of theirs are in this mess.
Are you considering divorce, only after you met this Escort or was it there in your mind before? Is this happening on the rebound?
You need to seriously consider the stigma of sex work, the increased risk of venereal disease, and the guarantee of infidelity. One important point you have conceded is that your to-be-wife will continue seeing her clients (old and new). You have already admitted that you are a fiercely jealous person and I fail to fathom how you are going to reconcile these two facts.
It is true that not all prostitutes deal with total strangers and many have regular customers. Here you will have to consider her views on sex, fidelity, and emotional attachment. There are people who act in porn movies and are still married. So, would you treat this as infidelity? This is a subjective feeling. Infidelity is a violation of a couple’s assumed or stated contract regarding emotional and/or sexual exclusivity.
An Escort’s Job is just a Profession like any other. There are Women who work in Bars, others may work as strippers, etc. Are you willing to look at it that way? You will have to make a massive shift from your narrow views that you harbor at the moment for your second marriage to be successful.
One serious consideration will have to be your Social Circle. Will they be willing to accept a Prostitute (you may not like the word) as your Wife? They will come to know at some time or you will have to live in dread of them finding out at some time or the other.
You will have to be totally flexible in your approach. You cannot differentiate between a past sex client and a new one. Your reaction when she told you she will be going to Italy is not a good omen.
You are obviously in love. I suggest that you first get a Divorce from your wife and then start living with your new Partner, before you think of marriage again.