I'm sorry you're feeling alone. I can sympathize, I've felt lonely quite a bit since C and I broke up. I think it's a natural part of a break up, to feel that void that isn't going to be filled, really, by spending time with someone else. Even if you feel the break up was for the best, there is still some mourning and grieving to do. I think a mix of spending time with other friends, and spending time solo and sitting with the feeling of loss and loneliness, is the best answer.
early forties, straight.