How can I find out if the physical pion of a woman 18 yrs my junior is going to last....or just a phase?

Am in a physical loveless marriage...for many years. Intimacy is VERY important to me and I have given up on trying to make this marriage work...have tried for years. Spouse has no confidence,initiative, desire or time, to initiate physical contact. Have had affair with much younger woman that adores me, wants me pionately...will do anything to please me! I enjoy making love to her, but will it last? I'm considering a divorce for the affection and pion that I need...and am offered by this younger woman. A lot of thought has been given in making this decision.