When I invited him to lunch he was embarrassed. He said sometimes. What does that mean?

My good friend recently invited me to lunch. I wanted to return the favor, so I invited him home too, but he was embarrassed and said first "but please come" and then "sometime". I feel more for him and he's so hot and cold, but I think he knows that I care about him, because even after a long trip he calls me to say he arrived safely and sends me photos when he's somewhere away from home. When we first met, he called me to go on an adventurous car trip with him. But the last few days I feel like he's running away from me. I don't know if it's because he's busy with work or if he's scared. He's nice to me, we meet almost every day, even if sometimes just for a few sentences. We basically text each other every day, just to say good morning or good afternoon and ask how we're doing. So I don't know what to think.

When I invited him to lunch he was embarrassed. He said sometimes. What does that mean?
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