1. OP:
has plenty of money, wellpaid job, enviable partner.
his #1 need is exciting encounters with more girls who love him as a man (despite him having a partner already), not for his money, so that both his ego and libido are taken care of.

2. Girls:
have good looks, nice figure, young pussy.
her top needs are better life style(read: more money), stable respectable job, and a strong but caring partner to have a family with.

The mismatch is plain for all to see, hence the relationship between OP and those girls won't last.