Just because your friends are back to their regular lives, it doesn't mean you can't hang out with them. Call them up for lunch or even breakfast. Maybe on your way to work, just after a friend has put her kid on the school bus. Or during your lunch break. I'd say try to see at least one person every week, if for nothing else to make sure you're leaving your home for more than just the necessities.

You could also try signing up for a class or join a group of some kind. Maybe an exercise class at the gym or a cooking class with the local community college. You don't need to go into it with the idea of making friends or replacing your ex. Just go in to be around other people having fun. I think if you focus on the things that make you happy, whatever your hobbies are, you'll feel less alone. Maybe your hobby will get you out the door. Or maybe you'll just get so absorbed in it, you won't be rehashing all the negative, lonely thoughts in your head.

One day at a time. You'll get there. You're very strong and very rational. You'll definitely get through this. It just takes time.