How do you get through losing someone who was your best friend first?

On week three after a breakup and I'm looking for people who've been through something similar, because I'm struggling.

Context: we were together around a year and a half, but we were close friends for a long time before that. She'd been going through a really hard time mentally for a while, and toward the end she told me she couldn't be in a relationship right now, that she had things she needed to work on by herself and didn't have the capacity for us. It wasn't a screaming breakup. She cried in my arms for what felt like an hour and a half. We both cried. She asked me to stay in her life as a friend. It genuinely felt like two people who loved each other letting go because one of them was drowning. I don't like to put a label on people but fearful avoidant is the most accurate description for her based on my own reading. And I guess I am anxious attachment.

Then within about a week she was in a new relationship with a guy from her new friend group, and it's moved incredibly fast, public posts, Instagram highlights, meeting family, the whole thing, three weeks in. Meanwhile I'm still picking myself up off the floor. It's like she's speed-running a relationship or something.

Here's the part I can't shake: I have this nagging gut feeling that something might have been forming with him before we ended. No proof, just a feeling, and honestly I don't know if I'm reading real signals or just looking for a reason it hurts less. I go back and forth between missing her like crazy, being angry, and telling myself none of it matters now.

I don't hate her. I still care about her and I hope she's okay. I just don't know how to move through this when the person I'd normally lean on IS the thing I'm grieving.

So I guess my questions are:

- Am I correct with thinking this is textbook fearful avoidant behavior?

- If you've lost a partner who was also your best friend, how did you actually get through the day-to-day?

- How do you stop yourself from checking their stuff / wondering what they're doing?

- Does the gut-feeling / not-knowing part ever stop bothering you, or do you just make peace with never knowing?

- For those further out, what did week 6, month 3, month 6 actually feel like? I need to know it gets better.

I'm doing the stuff people say gym, seeing friends, I even booked a therapist. Just need to hear from people who came out the other side. Thanks for reading.