I assume that your wife likes being eaten.
Next time when you're in don't let her cum first.
Pull out before she cums and release on her clit. If she asks while you pulled out tell her you were to excited and was trying to keep from releasing, and the best way to do that is to pull out for a while.
Better yet, fuck a little, lick a little, back and forth until she used to your eating her after some pumping.
After you release on her clit or in her cunt, lick her real slow without swallowing any sperm. They all love the slipperyness. she'll be shocked at first but tell her you don't mind so long as she gets a chance to cum. Your doing it for her, not yourself. Tell her you just couldn't hold everything in and that you'll try harder to let her cum first next time.
Remember, it's only kinky the first time.
i've done this with several women. They all protest at first and worry if you're going gay.
Last girlfriend, I didn't bother to waste time pretending. Second session, I never plugged in. Just kneeled between her legs, had her jerk me of while she was masterbutating her clit with the tip on my cock and then sprayed all over her clit. After cleanup, I thanked her for wonderful sex and told her next time she swallows me.
18 months later we were still eating and fucking almost every night. She never had a man that made her cum so good. never enjoyed having anyone cum in her mouth, but since I was OK with it she developed a love for it.
Just go slow after a few times she'll be asking if you would like some desert tonight.
Knew a woman that took 20-minutes of licking to achieve orgasim. Cum on on clit first, and she had a harder orgasm in two or three minutes. It reached the point where her asking for a quickey was a non-embarrassing way of asking for what she called a "treatment".
That's another strainge part of this ritual. They never ask you to jerk off on them. They want a "treatment"; "give you some desert'; "appetizer before dinner". Can't tell you how many times desert preceeded dinner. I'd walk in the door after work, dinner would be waiting, but desert came first, especially since they can cum so fast that way and have been think about it all afternoon.
Good luck. Be patient, they really do love it after a few times.