Frankly - it isn't the age difference; it's not even that he is physically repulsive (to me, at any rate), because a) we all like different types, and b) there are some very plain - in fact downright ugly - men who are very attractive; it's that he is a lazy, lying, vindictive, misogynistic, lecherous, bed-hopping, narcissistic sociopath who is likely to abandon his (current) family if "something better" comes along.
(In my opinion - I am not qualified to diagnose narcissism or sociopathy, but if I were I bet I would.)