Most US social media users engage regularly with multiple platforms. For LGBTQ+ people, this means making self-presentation decisions not just on one platform, but many. These choices are made in the face of sometimes-overlapping platform environments, which can have consequentially different norms, audiences, and affordances. Moreover, many LGBTQ+ users face high stakes in online self-presentation, due to the risk of stigmatization of their LGBTQ+ identity, increasing the importance of self-presentation decisions that enable them to achieve their goals and avoid stigmatization. This combination of environmental complexity and high stakes is not adequately accounted for in existing work on self-presentation, but doing so is important to support and understand the experiences of LGBTQ+ and other potentially stigmatized users. We adopt an ecological approach to an interview and cognitive mapping study of 20 LGBTQ+ social media users. We find that participants employ the platforms, audiences, affordances, and norms within what we call their "personal social media ecosystems" to avoid stigmatization while still allowing for expression of their LGBTQ+ identity and the flexibility to adjust their presentation over time.