Meeting an old christian friend whom I have lost contact for awhile..but I am atheist?

He's still a friend, so meet with him. Just avoid the topic of religion. If he brings it up, just say I don't want to talk about that right now. If he pushes, tell him you're atheist but make it clear you respect him and ask if he would respect your decision and that you can have that religious discussion some other time; today is a day to catch up.