Here are a few suggestions:
Brook: Brook is a UK-based organization that provides free and confidential sexual health and wellbeing services for young people. They offer a variety of online resources, including information about RSE, sexual health, and relationships.
Sex Education Forum: The Sex Education Forum is a UK-based organization that promotes high-quality RSE in schools. Their website includes a range of resources for young people, parents, and educators, including lesson plans, fact sheets, and videos.
Scarleteen: Scarleteen is a US-based website that provides comprehensive sex education and support for young people. They have articles, forums, and other resources covering a wide range of topics related to relationships, sexuality, and sexual health.
Sexwise: Sexwise is a UK National Health Service (NHS) website that provides information and advice on sexual health and relationships. Their website includes a section specifically for young people, with articles, videos, and resources on a range of topics related to RSE.