Personally I would understand, if a partner admitted this to me; but I know many guys can get sensitive over this issue. Only you know him well eneough too know how he would take it; if you do feel you need to get this off your chest with him, I would suggest you wait for a quiet moment when you are cuddled up with him, and then let your feelings over this come to the top. Then let him know something is bothering you, non verbally.
When he says whats wrong sweet heart, say you think something has gone wrong with your abillity to orgasm, and it's freaking you out. Tell him it happened for the first time, the last couple of times you had sex, and you are even struggling to cum when you have played play alone since. And say, our sex is and always has been so very good, but what is making me feel even worse is that I, did something I feel ashamed of; I didn't know how to tell you, so I faked it, the last 2 times ( you don't need to tell him how long it's been like this, but it will be the truth of how you feel). I"m so sorry, will you please help me try and get things working again, I don't want to be like this, I'm scared.
I wish you well, and I do understand, and I feel this would let you get this out of your head without upsetting him. But it's your call, and how you feel about trying this.
Then you can take it from there.