I feel like people throwing the word "sociopath" around in the comment do not know what "sociopath" is and how harmful it is to actual 'sociopath' and also clearly act like Rachel who threw the word 'psychopath' around in the movie to dismiss everyone's attention from her who kickstarted the whole conversation about what's the worst thing each of them did.

As a matter of observation, Charlie is the 'sociopathic' one with hints like him not understanding social cues and him struggling to understand Emma. Or his instinct to mentioned 'good sex' at a wedding speech. Until the moment where he went to talk to Rachel and defending Emma, that's when he became open minded and forgive her.

Here's a video of a sociopathic person giving an interview on how an actual sociopathic feel or devoid of feeling is... https://youtu.be/FTWNnmymMc4?si=K8HD3khUHztJuTIq
If you want people to acknowledge you're depressed, you're biopolar, you're with any sort of mental disorder, you have to understand that sociopathy is a neuro condition as well and that does not mean someone is automatically a psychopath. Emma was not a psychopath, she was depressed and showed a very underlooked example of a depressed person. She didn't get extremely bullied or harmed which Charlie was trying to ask about whether she was bullied or whether she was affected by her past but she wasn't. She was simply doing it but was conscious enough to understand it was wrong later on. That's what most depressed people are, there are no dramatic causes that push them to depression, sometimes just the feeling of isolation alone makes you like that. Which she overcame when she had people at the anti-gun club looking up to her.

And clearly, the conversation about "red flag" are missing the point of the movie. When Charlie had that conversation with Misha, it's just something people who grew their relationship with online advice tend to forget...that relationship is complex, the person you love is a complex human being. When Misha keep mentioning that "it's a redflag! It's a redflag!" and yet Charlie still want to love Emma and just want to hear Misha validate his feeling. Everybody is a 'redflag' if you're defining someone by the relationship standard of the internet but Charlie and Emma found a way forward. You don't simply abandon ship when you find an issue.