It certainly doesn’t sound disrespectful. It’s just a friendly greeting. Using a term of endearment in person is really quite different to addressing someone on an internet forum as “my dear” or even just “dear”.
It means the same as “honey,” or “sweetheart.” Older people who’ve been married a long time might call each other “dear.” Or a grandmother might call her granddaughter “dear.” I don’t know a lot of young people who call each other dear. It’s kind of an old fashioned word.