Not a sex therapist here, but I believe you need the advice of one. It seems to me like you conditioned yourself to link sexual pleasure and crossdressing. Until you break that cycle on your own (not sure if that is possible) or with professional help, nothing will improve. Your wife might perceive this as rejection of her without realising that this is solely your issue and you will keep chasing rainbows.
If I remember correctly, crossdressing and the surrounding behaviours are not considered a condition, unless it causes problems to the life of the individual or those around him. Then professional help is a must. I dont know whether your wife is happy with your sex life or not, but either way she is probably too young to be delegated to an optional extra to your orgasms. I can only view this from the female perspective and if there was an issue my partner had that was impacting my sex life, he would need to sort it out. Otherwise, it would have been a complete dealbreaker for me. If you can’t separate your crossdressing from your sex life with your wife, that is a serious issue.
I cannot advise on whether you should tell her now. The best time would have been 10 years ago, before she was locked with two kids in. The second best time will be after you talk to a therapist.