So I was minding my own business out on a run and suddenly realized the girl 20m in front of me was my ex (who had just broke up with me 3 days earlier). I had no time to react and just kept looking forward. Because I had dark sunglasses on, it looked as if I didn't even notice her, but I saw her looking at me and I know she knew I saw her because I had to weave around some dude (which made me come into her line of walking) right before (this is what prompted me to realize it was her). Honestly I desperately want her back, but it didn't really matter given how little time I had to react/not react. What should I have done? All responses welcome.
Also, this is a loop I run every day. What do I do if I see her again? I still like her so I don't want to be a dick, but I don't want to look desperate either. Advice?