I feel you. My ex-fiancee broke up with me on Thanksgiving while we were driving home. it will sting, but you have to accept that it happened first before anything else. You can't control others, so even though it might have come out of nowhere, you can't blame yourself entirely.
Consider and think critically about any reasons they told you to decide if it's something you need change. Think about the relationship itself and if you were content. My ex broke up with me for being unable to constantly mask my autism, seemed to feel bad for it after realizing the same thing, and then truly ended the relationship after I forgot to clean a dish 2 months later. Like yea, I definitely need to be better about remembering to do dishes, but I will never apologize for being autistic. Could you believe that I wasn't content in a relationship where my partner would get upset at me for reasons I don't understand? By the time I moved out of the apartment in March, I was already done grieving. Imo, if someone you thought you could marry breaks up suddenly and with little reason, they were too disrespectful to deserve you.
Finally, after the fallout, you need to rediscover who you are for yourself. You've likely been emotionally reliant on that person, which is ok, but now you need to sort out who you are after growing from that relationship. I've been going for long walks every day, listening to audiobooks. I've been reconnecting with college friends who I lost touch with during the relationship. I chose to treat myself with an expensive gadget. I've been leaning into my activism. You get to choose for you and yourself what to do with your free time, with no reason to coordinate with someone that may be uninterested.