WHY can't I get there lately?

Before I got married to my husband, no one had ever made me before. I could do it for myself, but no one had ever gotten me to the big "O" through any means. We have been married for almost 6 years, and until about year 3 he couldn't even do it for me. Well, he finally did get me there, and it was wonderful! However, lately I can't get there no matter what he tries. I have gone back to having to fake it because I don't want to hurt his feelings or make him think I don't feel attracted to him or something. I usually have to picture some fantasy I have or some other image. I have tried that, but still nothing. I can get myself there no problem with a vibrator or manually...but hubby is outta luck! What is going on with me and what can I do to fix it?? I really enjoy it more when he does it for me than the ones that I have by myself!!