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.
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 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.
Ash would be extremely hurt. He's a very loyal person, and having someone he cares about like Lillie betray him would be a huge blow. He might initially go into denial, not believing that Lillie could do such a thing.
Ash would be extremely devastated. Pikachu is not just his Pokémon but also his closest friend. He would likely first try to reason with Pikachu, not believing that Pikachu could truly betray him. He might be in denial for a while.
Ash would feel a deep sense of betrayal that could shatter his usually upbeat attitude. He might go through a period of self - doubt. However, his love for his Pokémon and his sense of justice would pull him out of it. Mewtwo, having already experienced betrayal from humans in the past, would be filled with a cold fury. It would use its psychic abilities to gather information about the betrayers. Ash and Mewtwo would work together, Ash learning from Mewtwo's insights and Mewtwo being inspired by Ash's tenacity in the face of 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 be heartbroken. He has a deep bond with Charizard, and seeing it turn against him would be like losing a part of himself. He would probably first try to reason with Charizard, thinking that there must be some mistake. When that doesn't work, he might become a bit angry, but mostly he'd be sad and determined to find out what's wrong and fix it.