If EVERYBODY in your life hates your significant other then they are the problem. If it is one or two people like a family member you have a turbulent relationship with and one friend who’s always been kind of jealous, maybe they just hate your success. But most of the time that is not the case and the people who are closest to you and love you and have had your back for years probably know when your new relationship is toxic and/or doomed.
“My friends don’t talk to me anymore because of my boyfriend.” Who do you talk to now, other than him?
YES. A MILLION TIMES YES.
Inverse also true! If your partner dislikes most of the people you are close to or gets really pouty about you spending some time with them and keeping in touch, that's a huge red flag.
If you don't have people over anymore or don't take your partner places because your partner's behavior is embarrassing or noxious, something is very very wrong.
So this is crystal clear to me now, in hindsight because, y'know.. But also add on to that list 'I don't want to talk about my relationship with my nearest and dearest because I feel like I have to defend it' is also something to look out for.