Part of it may be that he was cheating on his wife or perhaps she felt in a way that he was cheating on her, but I think more importantly they had a special bond that got tainted.
The very first time Bob Harris and Charlotte are in the hotel bar he catches Charlotte's attention by 'applauding' the singer in a mockingly fashion. That's when they first started bonding because she saw him as someone like her who could 'see through the whole charade'or something. When he later sleeps with that same singer he's in a way tainting that bond between them. That's my take on it anyway.

No I don't think she was in love with him either. Maybe she just felt like they had a connection and didn't think he would sleep with some other woman after all the time they were spending together.

She was jealous, she was mad he slept with the Jazz singer. By the end of the movie he could have taken her back to her room and slept with her. Yes she was jealous. I don't think she was really in love with her hubby either.

I got the impression that she was jealous. I think she liked Bob because he gave her the attention Jon never did

This message has been deleted.

Exactly.
It wasn't all romantic jealousythey're both married, and she's smart enough to know that she didn't really have a right to be jealous, but she couldn't help it. She thought they, as two American strangers in Japan, had bonded in a unique way.
What Bob did wasn't just pathetic, it was PREDICTABLE: a middle-aged celebrity with a troubled marriage has an affair with a woman he meets in a bar. Ho hum. It was such a cliched way for him to deal with his problems as opposed to what he and Charlotte had going on. I think that's why it really bothered her so much.

she even mention it in the film " let never come back again here b/c it will never be this fun" it was much like rick saying to elsa in casablanca " we will always have paris " they had "their" moment , she was hurt that he would spoil it .

It seems like Bob himself was very shocked and disgusted by himself upon waking up to realize what he had done. Maybe he had too much to drink? Either way, I think he could have explained himself better.

I always thought that what she felt was rejection.
During that scene she says "Well she is closer to your age".closer than Charlotte is? "Talk about things you have in commongrowing up in the 50'smovies you made in the 70's"
It's as if she is expressing excuses/reasons on why Bob chose the lounge singer over her. I think she wanted an answer.
Would Charlotte have slept with Bob? Who knows. But she felt a connection and closeness with Bob that when she discovered Bob's fling she was hurt.

She was jealous of her importance to Bob, thinking that what the had was special and he had tainted it.

I took it as she was jealous

She was "involved" only with her husband. She was showing disapproval like a good female friend would, knowing he has a wife back home.
.... TxMike ....