My old friend is trying to get in touch, should I let her?

You said "I wasn't even thinking about them at all" but to me it sounds like you think about your old friends quite a bit. It is normal to miss the people you've lost, but you can't get stuck living in the past. What's done is done. The what ifs don't matter. My advice to you is to move forward. You said you've made new friends already, you just need to realize these people want to open up to you and be a good friend. One day a few of these people will become just an old friend you never see anymore, but people come and go, things change all the time, you've got to live in the moment and enjoy every second of what you've got now. One day you might look back and miss jumping at the opportunities you have in front of you right now. Take life one day at a time, and always look forward. You can't change the past but you can change your future. Just keep smiling.