I know a live example. A hot girl I see often in the gym has a boyfriend, I know the guy, a secure good looking dude with obv plenty of female action in his life.
The girl has a personal trainer also, they train in the gym I train and excersise outside in parks. I asked him a week ago do you mind that shes so busy with her body and hanging around with that personal trainer so often.
He said no man let her do what she wants, he keeps her motivated and she needs the attention during training, im not giving it to her and she pays for it herself. On top of that, even if something happens between them I doubt it will but iff, I got 5 other girls texting me right now so no sweat, she knows that I can get new p*ssy in a blink lol so if she wants to keep me she wont do something stupid and he changd the subject like he really didnt care.
so theres your answer bro... spin plates and keep your options open always especially with the hot women
and from my own experience, if a girl wants to cheat she will do it, personal trainer or not eventually offcourse it could happen easier with a trainer so physically involved, but it will happen if shes not attracted to you anymore so I wouldnt mind so much and focus on yourself