Is it constantly like this? For me it's been almost 4 months since she left (almost 6 since she told me she wanted to leave)..I have moments when I feel like that but as time went these moments came more in spurts than an actual state of being.

If it's constantly like this, maybe you should go see a therapist or speak to someone you trust to help you. You might be suffering from depression, it's very possible it's not actually about him at this point.