There are many people who want to keep their work life and personal life separate. For that reason, they’ll often reject the social media requests of co-workers. In that case, it’s not personal.
I think it’s harder to become friends with people you work with. You have the extra dynamic of the hierarchy at work that can make social interaction outside of work very awkward. I would strive for friendly interactions at work, but not necessarily look to make those people friends outside of work. And don’t take a rejection of something more personally (I know that’s easier said than done).
Rejection sensitive dysphoria could be magnifying this for you as well:
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ADDitude Community Moderator, Parenting ADHD Trainer & Author, Mom to teen w/ ADHD, LDs, and autism