what happened to break her heart that she can't trust you?
I'm going through a separation (although more serious). I've been married for 9 yrs with 3 kids. My wife & I have been separated since January. But your situation is still hard after dating 3 years! All I've read about separation is this: don't force things, especially on a woman. Women take a while to heal when they're wounded (I don't know about your case).
My wife told me it's like she has a cast on for a broken bone and will take a while to heal.
I've been adviced by a counselor to not initiate contact for a while. Let her be the first to reach out. Of course, if months go by without her reaching out, that may be a sign the relationship is over. It's encouraging she still loves you, that's significant. She still care about you and isn't willing to give up!!!!
Have you two talked about marriage in the past? Wow, 3 years is a long time to date. Hang in there. Ask yourself if she's the one you want to spend the rest of your life with, it will make the pain of waiting for her more bearable.
You are not alone. Lots of couples & marriages go through separations. It's more common than you think. Being in a committed relationship is not easy, that's why so many of them fail. But the dedication is worth it. This separation has the potential of making your relationship so much stronger. When it's healed, it will be stronger than ever possible before.
Keep us posted.