A little late to this thread, but the story of my life.. latebloomer. I was drawn to this, though, because I am a W and Honesty and Openness is my #1 EN. My H claims tho, that I make this hard because I invalidate his feelings, when really i am just trying to have a discussion about where those feelings come from. Still, I am trying to be more careful about my responses.
I am with those here that say "Tell her", but be careful. Just from my own experience, I WANT my H to share a lot more, but not to make me feel guilty - he really is good at THAT-. And I agree with whoever said to be careful not to instill doubts. You don't want her to feel that either of you made a mistake, just that you are HUMAN, with human doubts and insecurities. I have to admit that some of our probs are from my insecurities, as well as his. I wish that we could figure out how to share these and introduce them healthily into the problem-solving! I hope that you can do better in this situation than me and my H.
Anyhow, enuf rambling, I really think that you should find a "safe haven" and tell her how you truly feel. Try to get across that these are merlot ramblings in a way, and not necessarily over-riding thoughts all the time, but they are there sometimes, nonetheless. AND, how much you appreciate that she loves you in spite of your human failings, or thoughts of insecurities.
I think that most people go through a period or two when they aren't sure that they are "Good enough" for their significant other. Just don't use it as an excuse for anything. Or to blame. Being introspective and deep is nothing to be ashamed of, that's for sure.
JMHO,
jls