Relationship help!

Hello! I am feeling so lost and unsure what to do so I am looking for advice, especially if someone has gone through this or something like this before. Thank you in advance!

I have been with my girlfriend for almost two years, knowing her for four. Out of no where she recently started pulling away, just for a few days. Leading up to this there were no signs! We were planning our future! fantasying of what it will be like when we live together. We both have kids so it is a two year plan. So very slightly. Just a vibe shift I could feel through text. I had just had a good weekend with her so this made me very uneasy. Then last Friday, we had plans. But early in the day she instead asked that I meet her out somewhere. That Something wasn't right and she wanted to make it right. Instant stomach dripping punch to my gut! I said of course I would meet her anywhere anytime but please not to break up with me! In the past she has broken up or more like semi broken up with me, when she has had added stress in her life. We have always been able to talk it out and stay together. I met her out Friday and instantly her vibe was so different towards me. Almost cold. She stated she has felt something off the last few weeks, and the last couple of times we were intimate. That she needed time and space. That me being her first official WLW relationship maybe she needed to explore. That we have not been good at communicating wants and needs in the bedroom and that it should come naturally if we are comfortable with each other. I have always struggled with this in my life, any partner but have felt closer and most comfortable that I have ever been with someone.  I pretty much begged her not to do this. But that I would give her space. I really think we can work this out, I need to push myself out of my comfort zone. I have been so lost! I have written her a long letter. With all my heart, all my thoughts. I do not know how she will receive it. Will she be annoyed because its stepping over the line of space? Will she appreciate all my honest words? I just don't know what to do. Any advice will be appreciated!