My opinion about your working:
What do you do all day? Yoga, flower arrangements, TV? Your DS is 15 and you have a cleaner, a gardener and a dogwalker.
Yes, we also have cleaner/housewoman and a gardener. But I work (a lot!), DH works part-time (mostly from home) and we have a toddler and soon a 2nd baby...
A part-time job is something I personally would expect from somebody in your situation. It seems like you have a very comfortable lazy life.
Secondly: Do you want to be in a relationship with this man? You didn't sleep with each other for 10 years.
And whilst this doesn't justify cheating... Well, I personally wouldn't be ok with this.
Do you want to start sleeping with him again? After 4,5 years of him having an affair? If no, would you be ok with him having an open relationship?
If the answer to that question is also "no"... Well, I think breaking up might be better. Seeing as he apparently doesn't want to live without having intercourse with somebody... Which is understandable, imo. (but still doesn't justify the cheating!).