If Ash found out about May's crush, he might be a bit confused. He values May as a friend and traveling companion, but he may not have thought about her in a romantic way. However, he would probably be kind about it and try to make sure he doesn't hurt her feelings. He might start to see May in a new light and notice all the little things she does for him that he didn't pay much attention to before.
Ash could get angry. He has a strong sense of justice, and he might feel that May has violated their friendship. He could challenge her, not in a violent way, but more in a way to get an explanation and to try to make her see the error of her ways. He would likely be determined to show her that what she did was wrong.
I think Ash would be angry as well as hurt. He's a passionate trainer and his friends mean a great deal to him. He might challenge May in a Pokémon battle, not to defeat her but to make her see how wrong her betrayal is. And during the battle, he would keep asking her to come back to their old friendship.
Ash would initially be heartbroken. He has shared so many adventures with May, and this betrayal would shatter his trust. He might go off on his own for a while to think things through. When he comes back, he could be more determined than ever to prove himself without May. He might also be a bit more cautious when it comes to making new friends. His Pokémon would sense his distress and try to comfort him, but it would take a long time for him to fully get over May's betrayal.
Their friends like Brock would probably be very excited. Brock, being knowledgeable about Pokémon and also having a nurturing side, would offer all kinds of advice on taking care of May during the pregnancy. He might even cook special meals for her to ensure she has all the nutrients she needs.
Ash would likely be shocked at first. He's so used to seeing the good in people, especially fellow trainers. But then he'd probably get angry and determined to set things right. He has a strong sense of justice, so he wouldn't let the betrayal go unpunished.
Ash would probably be very shocked and hurt. Pokemon are like his family, and for Misty to steal one would go against everything he stands for.
Ash might be heartbroken at first. He'd feel a deep sense of loneliness and confusion.
Ash would probably be initially shocked. He is used to seeing the good in people and would not expect such a betrayal from Cynthia. He might stand there in disbelief for a moment, unable to process what has just happened.
Pikachu might be very confused at first. When it sees 'Ash' (really May in Ash's body) acting differently, it could be hesitant to follow commands as usual. For May's Pokemon, they might be surprised to see 'May' (Ash in May's body) suddenly having a more battle - oriented attitude. For example, May's Beautifly might be confused when 'May' wants to train it for battles instead of focusing on its appearance for Contests.
The Pokémon community around them would probably be quite shocked at first. Their friends like Brock might be both surprised and happy for them. However, some of the more traditional Pokémon trainers might frown upon it as they are quite young. But Ash's close friends would most likely support them and help them out, like providing a place for May to rest during her pregnancy.