Damn 8 years is a pretty long time, how long has it been that he isn't talking to you much? And how were things before did he talk to you more, interact more and seem more into the relationship? Also when you try talking to him to get him to interact with you what kind of reaction does he have? Like outright ignoring you, or just seeming disinterested?
I would say you'll probably have to talk to him about it, and explain your concern granted it wont be an easy conversation but sounds like it needs to be had so you can better evaluate the situation and decide if leaving is the right choice.
It could be something else on his mind to, making him seem distant to.
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We won't go back.