Dude you really shouldn't be afraid of those kinds of things. Whenever you think about that stuff think about how many couples end up divorced? I'm just saying you need to focus on your life, and making yourself better and stronger, and if you do that happiness will come and find you. I was scared too when I broke up with my girl.
I was always anxious about going out to bars and stuff or talking to other girls, since I'd been dragged around on a chain for 3 years and never had to worry about that, but once I took that initial step, acted like myself and went out and did it; Let me just tell you once that happens you're first thought in the morning will not be holy crap I miss her, it will be holy crap life is awesome and I feel sorry for the next guy that has to endure that crap form her. And who knows that new girl could be right around the corner, but don't even be concerned with that, just try to occupy yourself and always think positively, it can help you go very far in life.