Well a pro is definetly that short-term you get what you want! But depending on what kind of person you are, feeling of guilt might eat you up or just bother you, or it doesn't affect you at all

Also think of the trouble when your wife finds out! I can't imagine how you think of your wife after 7 years being together (if there's a sexual problem, or if you feel of her not being good enough anymore after you muscled up, or if you just need variety in your sex life, etc etc) but have you considered being honest with your wife?
Is she conservative and making out with other people is a no-go? Or might she understand if you told her? After all if she understands and lets you do what you want, it will just strenghten the connection between you too.