Should i start talking to get again?

[JV]

So today is my birthday and i got this notification on Facebook of this old friend that i met in MySpace and become really really close. She always being there and so have i for her. But we don't talk at all no more for over two years. Seeing that post made my day even brighter i feel like she still cares for me. And im shy saying something back through Facebook. We went out once but i knew that wasn't a good idea for the future if we break up. I knew our close relationship would go away and i was right it did. Her sister made me go out with her she like me but i wasnt ready she told me how she felt if i wouldn't go out with her sister made me feel bad knowing she would be sad every time i said no. So i went for it things wornt there same. Then i broke up and it all when down. 6 months later i started talking to her again she would reply days later instead of 30 seconds like she use to. And today she remembered my b-day. I just don't know what to do i really think i should start again. But part of me say to let it go. What's your opinion?