I have some advice, tell your wife how beautiful she is, keep telling her all the time, I believe many if not most women really lack confidence, and they love to hear someone, especially someone they love tell them how beautiful, attractive, smart they are. You may have forgotten since you have been together so long. Then start to make it sexual, getting her hot and turned on, play with her, kissing her, finger her, anything. Learn to serve her, many men never learn this, what I mean is learn to please her sexually, I mean really please her. Women usually love to be eaten, but will never tell anyone, let alone ask for it. If you do this often, she will get more confident, and maybe even tell you she wants you to eat her. You will know for sure when you do, there will be no doubt. Then start to tell her your fantasies, she will want to know, she probably has many of her own, but women are so self conscious and they immediately think they are perverted. Ask her what are her fantasies. Make certain she is getting hot and have sex with her often, she will start to open up and want it often, then start to slip in how you think it would so hot to see her in action with other men, how hot it would make you, how it would make you want her even more. What she would be hearing and starting to understand is that you would not think her bad for doing this, but that you would find her even hotter. Mention maybe going to a swingers club, that it may be fun. Buy her sexy clothes, always telling her how hot and sexy she is.