Hi , I'm currently going through this myself with my partner. I understand completely how you're currently feeling.
I met my partner 9 months ago , officially been dating for going on 6 months now.
He basically switched over night , however I did see little sign's a month leading up to where we are now. I think the hardest part for myself is that I had no pre warning. He had explained bits of his previous abusive relationship and now looking back on the things he was saying to me with a better understanding of what his going through he did try to explain how he was feeling but his communication wasn't very clear. I feel terrible for not understanding him but have to also give myself grace. I just didn't understand what I understand now. We are basically very much in the same situation as your relationship. I'm constantly going through mind loops myself , back and forth from does he not love me anymore to this isn't about me give him time and space. It's that constant battle between doing the things he loved me doing ( such as daily messages ) to now respecting the space he has asked for. It's definitely a hard situation especially when it's the first time and not having the tools in place to navigate this. Waiting and praying he can find his own way out of survival mode to be able to have a conversation about how I can best support him or even just anything to understand more about what he is dealing with. It's hard to speak with anyone else people don't really understand. Family & friends love you so in their mind your partner is just being a terrible person , however you know differently and you hold so much love for this person that you truly don't want to give up in their time of need. I'm not sure if this is allowed however if you would like to reach out I could definitely use a friend who understands and is going through the same thing. I haven't spoke to anyone about my situation I struggle with it because I know right now he lacks trust in me, but deep down logically i know i am his safe place.I believe this is all part of his survival tactics because his irrational thinking and the fact he doesn't even understand why or when he started feeling this way clearly explains it. I just can't walk away from the man I love right now even if his walking away from me. I need to try at least and I truthfully believe he will be ok. His such a smart , determined person. Right now im praying alot , seeking my own mental health assistance, learning about ways I can better support him when he comes around. I'm also back at the gym and doing my own work to insure I have clear boundaries and better ways of coping in the event that it will most likely happen again.