Issues with understanding my partner

Hello, i am posting this to see if anyone has any useful tips or tricks that they have found helpful in any way regarding opening up.
So a bit of background. I am a 19(soon 20) year old male with Asperger. I have been aware of my condition since the age of 8, and now have gotten into my first serious relationship. We've been dating for 6 months, and things have been very rocky towards the latter months. She has been very upset with me at times, for not understanding her feelings or taking her into consideration, which i believe that i do all the time. It simply seems that we don't understand one another. She is aware of me having Aspergers though.
Anytime i try to open up to her, and talk to her about things that are on my mind, i seem to simply go into shutdown mode. I can share a bunch of things with her, but a lot of things i can't get myself to tell her. This is happening with anyone i try to open up to, and it's really affecting our relationship.
She hasn't ever done anything to NOT deserve my trust, but for some reason i simply cannot get myself to open up to her, even if she is a person i truly respect and trust.
Any help/tip/advice anyone could share would be very welcome. Thank you all for your time!

my guess is that you can't open up because you're concerned you'll get some form of negative reaction. my best advice is to write her letters and see what response you get.