Why is he ignoring me?

There's a guy at work. I know him quite well and sometimes i'll drive him home. He used to be really chatty with me but know he seems to be ignoring me, speaking to me only when he has to. He's friendly when he does talk but only does this in the company of others. I haven't worked with him for some time so haven't really had chance to speak to him in detail but we have crossed paths occasionally in the office kitchen. He was so nice to me when i first started working for the company but now it seems he can barely stand to be in the same room as me. Worst of all, i keep having dreams about him and am beginning to realise just how much i like him. Any advice folks?