It would appear they are very happy and he is smitten/faithful so maybe I have rushed into judgement in the past, however, he could cheat/punt again at any time and my friend is more than aware of this, old habits do die hard after all.
I think it's easy to have such a nice relationship during the "honeymoon period" / falling in love stage where you only see the promise of their future together. After that sweet stage had gone passed, the laws of the "relationship" still apply to anybody (whether you are escorts or not) e.g. compatibility, personality, how he/she could handle the day to day reality / stress, how will he react when monogamous sex is no longer so fresh / exciting, etc. Mother used to say, "there is no eternal love". I would rephrase, there's no eternal "romance" - the initial falling in love stage does not last. There are loads of men, who would confuse "love" with some exciting sex / fun and romantic nights out and in. People do get ill, so as escorts. Will he be there if you became ill? Will he move onto the next glamorous escort, telling her "his wife won't give him any sex at home"? These may be worth thinking. You could be the next "wife / GF" who won't give him sex at home. History can repeat itself.
It all depends on what you are looking for in an LTR or if you actually want LTR e.g. investing time, energy what else? Pressure from society? Most of us, mature ladies had done all that a few times already and wore our T-shirt. I often think "I got better things to do" whenever I get asked out. Do I want to go away on a holiday with him / Do I want to spend the whole week with him? We all learn from our past mistakes. Having said that, though, wanting love is probably part of our female DNA (what makes us human). If "romance" is working out, just enjoy. Make the most of it. But it's always useful to be realistic about 'Men'.