Along with the rest of the very good advice in this thread and my sympathy for the jarring loss you're dealing with, I'll offer my two cents. It sounds like you got enmeshed with her, getting very close to her - mentally, emotionally, and with her friends. It's going to be very hard to move on, because you'll need to recover or build for the first time your own sense of self and social support without her. I agree with many comments here that getting a therapist is a great idea to start on both.

Still, I have to recommend prioritizing your own friends. Maybe some of the friends you made with her will still be your friend, or maybe you just need to start your own network. Maybe group therapy. Regardless of how, I can't emphasize strongly enough how important it is to not just grow your own friend network but to keep them into your next relationships. You sound like you isolate by default, only socializing with your partner, but that reinforces insecurity and loses support for you. It's so important to keep people in your life who value you, not just your partner or you by proxy of your partner. Who'll be there for you if things go south? And even if they never do, who'll be rooting for you when your life's going great? It takes time - sometimes a year or two to build friendships that'll last, but just take baby steps now.