It Will Get Easier
First of all, I'm sorry that you were raped. It's a lousy, horrible trauma. You don't say how long its been since your attack. I'm assuming not too long, otherwise you'd know a little bit more how to deal with your issue. Please know that as you continue to recover, everything -- including thorny issues like this one -- will become easier for you.
You're Not Required To Divulge It
Here's an important message: you're not required to tell anyone anything about your rape. Ever. It is always your choice what to say and when. That's the good news. Unfortunately, the choice can seem pretty daunting.
Only Use It To Explain Your Behavior or Attitude
My advice is, don't bring it up unless it becomes necessary to explain your behavior or your attitude. You know how much contact and sexual/intimate relationship you are ready for, or ready to try.
If you find yourself freaking out if he touches you a certain way, or tries to kiss you and you're not ready, or makes a comment that upsets you and it's because of your experience being raped, you will need to stop and say "y'know, that makes me really uncomfortable. I was attacked recently, and it freaks me out when you....." Any half way sensitive guy will adjust to make you feel more comfortable.
You Control the Amount You Reveal
If he wants to delve into it more and find out more about what your attack was, and how it affected you, he can bring it up. Then you choose whether or not you want to reveal more to him. You're always free to say "I don't want to talk about it anymore" or "not now".
After I Was Raped
After I got raped, I found I had to explain things to a couple of guys I dated after. I tried to kiss one guy and freaked, and so had to tell him that we needed to slow down. He understood. Another time, I had to ask a guy not to ever, ever grab my hair, and never ever come up behind me. He had done it and I nearly went ballistic! He understood as well, and didn't think any less of me.
And then, I remember the time when I was walking with a guy I was dating (now my husband) and we were about to pass a bunch of guys in front of a convenience store who looked like my rapist. I kept asking him to cross the street with me, to go faster, to get me out of there, and he wouldn't. So I fell apart on him, and had to explain that something as "innocent" as passing by some people was a trigger to me. He understood, but it was rough to go through it.
No "Full Disclosure"
There's another part to your question, though: are you required to confide in a guy you're seeing, like you need to have "full disclosure"? The answer is no, no matter how long you've been seeing him. Again, it should be totally your choice who to tell and when.
Is He Your Confidant?
If this guy you're seeing seems like he'd be supportive, and a helpful person for you to confide in, by all means go ahead and bare your soul. Get help from whoever can be of help to you.
But don't feel like you have to share your experience as part of some weird need for disclosure, or because you feel you're "damaged goods", as though he might not continue to see you if he knew.
Be Proud of Yourself
What happened to you was not your fault, any more than if you had been robbed at gunpoint. There's nothing wrong with you for having been raped, and no need for you to "confess". You can still be proud of yourself and what you have to offer a guy. Being raped affects you and changes you somewhat, but it doesn't put you in some "bad" category as far as guys are concerned. Almost all rape survivors date, fall in love, get married, and have relatively healthy experiences with men.
Hope you have a good recovery -