The different titles and schooling is almost dependent on where you live. In the states they have different criteria that you need to meet in order to counsel others in terms of sexual health issues. Some people are sexologists, some are sex therapists, some are sexual health professionals, some are just psychologists, psychiatrists, social workers ect, ect. They have become a lot more strict and organized in providing certificate, bachelor, masters, and PhD programs so that people are receiving accurate and professional help. At least that's what I understand of it.. Could be wrong.
DBD. I would say in general, it's synonymous with "sexpert" and does not specifically mean a certain degree or experience but one who is considered expert in the field. However, there are degrees catering to sexuality, now, and some schools are calling them sexology degrees so that would be a more.. standardized definition, I guess.