Sakura would probably be really concerned. She has known Naruto for a long time and would want to make sure he's okay. She might try to talk to him and get him to open up about his feelings.
Shikamaru would likely be the voice of reason. He would analyze the situation and might tell Naruto that break - ups happen and he needs to move forward. He could also offer some practical advice on how to deal with the emotional turmoil.
Kakashi would be more of a silent observer at first. But he would be there for Naruto if Naruto needed someone to talk to. He might share some of his own experiences with love and loss in a very understated way to help Naruto understand that it's part of life.
His friends would be really happy. Shikamaru would probably be like 'Well, it was bound to happen eventually, Naruto.' and offer some practical advice. Choji might bring over some delicious food for Hinata to help with her pregnancy cravings. Kiba would probably joke around with Naruto about how his life is really changing now.
Sakura would be really happy for them. She has seen Naruto grow and has always wanted him to find true love. Since she has moved on from her old feelings for Naruto, she would be supportive and might even offer to help with the wedding preparations. Shikamaru would probably be a bit lazy about it at first, but deep down he'd be glad for Naruto. He'd say something like 'What a drag, but if it makes you happy, Naruto.' Kiba would be excited, especially since Hinata is his teammate. He might tease Naruto a bit about finally getting the girl.
Their friends would be overjoyed. Sakura would probably be really excited and offer to help Hinata with any medical advice during the pregnancy. Shikamaru might give Naruto some practical advice on how to handle the added responsibilities. Kiba could be really happy and joke around about the new baby being a future ninja partner for his own pups. And Ino would be eager to plan a baby shower for Hinata, full of beautiful flowers and gifts.
At first, Naruto would be stunned. But being Naruto, he'd quickly gather his wits. He'd probably joke around a bit to lighten the mood and try to get Hinata to open up. When he realizes she's serious, he'd start to analyze the situation. He'd think about what could have made Hinata do this and try to find a solution that would not only free him but also help Hinata if she's in some sort of trouble. He might also think about how this would affect their friends and the village as a whole.
At first, Naruto would be completely shocked. He has always seen Hinata as a loyal friend and someone who has deep feelings for him. So the idea of her betrayal would be hard to fathom. He might try to deny it at first.
He would be filled with rage. Naruto has a strong sense of justice and the fact that someone took Hinata away from him would fuel his anger. He would vow to find and punish whoever was responsible. He might even become reckless in his pursuit of vengeance, endangering himself and those around him. His friends would have to step in to try and bring him back to his senses.
Naruto would probably be heartbroken. He loves Hinata deeply, so finding out she might have cheated would shatter him.
Naruto could be initially in shock. Given his strong feelings for Hinata, he might not believe it at first. He could try to talk to her and ask for reasons, hoping to fix things.
Hinata might be shocked at first. She has always adored Naruto, and this sudden act of aggression from him would leave her stunned and unable to process it immediately.
Shikamaru, being the more laid - back but perceptive friend, would likely be disappointed. He might see the signs that led to the divorce coming from a mile away but feel powerless to stop it. He would probably just sigh and say something like 'What a drag' while still being there for both Naruto and Hinata as a friend.