Guy's Behavior

What does it mean if a coworker that used to tease me and have playful conversations with me suddenly acts all cool and nice now?

This guy at work used to tease me and we would always talk about silly things, and then I left the city for 3 weeks and now when I have come back I feel like the vibe between us is different. He was acting so cool and chill and instead of talking about silly things he talked about how his family is going to move and how he does not now what is going to happen in the future. What does thing change mean? Doesn't he like me anymore?
What does it mean if a coworker that used to tease me and have playful conversations with me suddenly acts all cool and nice now?
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