Masculinities and femininities are often characterized by social inequalities and mainly studied from the perspectives of adult, heterosexual and non-activist people. This study explores the discourses on masculinities and femininities of young cisgender men and women, involved or not in feminist activism and of different sexual orientations (heterosexual, bisexual and homosexual) in Spain. Between 2019 and 2020, we conducted a qualitative study with 20 semi-structured interviews and 8 discussion groups in which 73 people participated. A socially dominant gender discourse was identified, which establishes a dichotomous understanding of masculinity in constant confrontation with femininity, as well as of heterosexuality against homosexuality, in a heteronormative context. Young people discursively position themselves differently from said discourse according to their sexual orientation and involvement in feminist activism. We encounter discursive positions that reproduce the socially dominant gender discourse, especially detected among non-activist heterosexuals. We also observe others that try to transgress it, mainly among activists of all sexual orientations and non-activist homosexuals and bisexuals. This study empirically adds to the knowledge of the configuration of inequalities in gender relations and how interactions with sexuality take place. The results also provide guidance for future gender-transformative interventions to promote gender equality and social justice.