I don’t understand his behavior?

We are group mates , colleagues, and we are going to work in USA in this summer.(abroad)
We see each other 5-6 hours a day, he calls me in the evenings , and we talk 2-3 hours there.
He never says “i want you to be around “ but he does everything to make me be where he is. He found me this work , where we work together now , he asked me to join him for this trip to USA.
But he always says “we are nothing to each other” , “I’m nothing for you”
Yes I understand, may be I didn’t do so much things towards him , but I’m always showing that i value him , always agree with anything he asks me about. I try to be closer everytime, but he pushes me away when i do so. But if he wants so , he does and says a lot cute things to me , i accept his lovely moments, even though I noticed that he is shy about showing me his emotions, he can say like “i missed you” and then delete that message. Or say “you’re perfect” and joke around as a friend.
He always here with me, any time , always protects my safety, helps me.
But when it comes to feeling, he never says it openly. I don’t know who we are for each other.
Sometimes he can ignore my messages, be cold to me , without any explanations. I really don’t know how to behave in this situation
I also have feelings for him , but I don't know does he have
He makes sad when see me with other guys.
I don’t understand his behavior?
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