I think you need to be open with your wife about it. Sit down and talk, explain what's going on and then let her know that you don't want to make her feel like she's a sex object etc. it sounds like that's not the main issue here, it seems that the number one problem is how ashamed you are of it.
It's a natural thing, we're human beings out on this earth to procreate after all, and she's your wife I'm sure she will understand and appreciate your honesty and you can decide between you what the safest way to deal with your frustrations are. Good luck!!