He has already give up on chasing me, how can I move on?

Remember why you held back before, and dig into those feelings.

" none of us are willing to take the first move"
Maybe he just got tired of it all. Maybe he's waiting for YOU to really chase him.
Ask him out again. You will get your answer then.

You may be right. I asked him for joining an event with me few days ago. Although he rejected as he had plan on the same day, he did mentioned another similar event in the coming future. I guess he may want to hint me that we can go tgt. He became much more friendly and caring after that, just like what he did when he tried to approach me before. However, I still don't feel comfortable to flirt or show obvious signal to him in the office. Maybe he is not secure enough as I rejected him few times before, he acts hot and cold now. I don't think confession is a proper way to tell him how I feel as I don't want any embarrassment btw us if his anwser is no. But I really want him to know my true feeling. Our vague relationship has been maintained nearly a year, our feeling can die out easily in this stage. I don't want to regret simply because I haven't try hard enough... What can I do?