Why is my workplace romance not developing into something more?

I like this guy. We work in the same office. He constantly messages me during work, stares at me all day, offers to have lunch with me etc but getting him to meet up at the weekend/take me out he hasn’t suggested or when I have suggested we go out he ‘already has plans’ and when I asked ‘when are we meeting up at the weekend ‘ he said ‘you will know when ‘ so I’m just a little confused as to what is going on. We flirt heavily at work and he does sweet things for me.
Why is my workplace romance not developing into something more?
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