What does it mean when my ex says this?

He said he hasn't been talkative because he has a lot on his mind and will tell me about it when he sees me this means he's suspicious about something? He said he’s thinking about me. What does it mean when he says he has a lot on his mind?

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What does it mean exactly when he says he has a lot on his mind?
What does it mean when my ex says this?
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