What are the signs my boyfriend has a crush on a co worker?

We have been dating for almost 2 years and I have this 'feeling' that my boyfriend has a little bit of a crush on a co worker. He said he thinks she has a crush on him, and she might. He is handsome. So I snooped and I see that they email almost everyday. Things like do have anything to eat? I don't want to move my desk? She will email him and he will respond but with short direct answers. There is only one email so far that he has conversed with her a little. When he talks about work everything checks out. I don't know if they go to lunch together, I try not to think about it. I need some advice, am I just being an insecure jealous girlfriend?
What are the signs my boyfriend has a crush on a co worker?
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