Guys, My boyfriend is acting strange, Maybe its a man thing?

I'm normally pretty good at detecting when something is wrong with the people I love and although my boyfriend has been really lovable and spends so much time with us and is just amazing in every way, I can't help but shake something is off. I dont think he is cheating or anything like that but when I ask him why he seems down or deep in thought he would say that I wouldn't understand.
Now this isn't the first time and normally he would say things like 'he is dealing with it' or ' you won't understand' or 'I dont want to drag you into it' etc. It worries me big time as he would be completely fine and then when he isn't busy he would start thinking like a lot about all kinds of things. I dont want to push but I also feel like I need to know whats happening. He says I am a good distraction for him and he loves spending time with me which he does but obviously my mind is going all over the place very worried of what is going on that I dont know about. He knows I am there for him and i dont want to force him to open up to me but its really getting to me now.
Im a woman, I dont always understand how the male brain works and I know pushing a man can end up hurting him more or our relationship... Guys, what can I do? or is this normal?

Guys, My boyfriend is acting strange, Maybe its a man thing?
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