It might help to start in the spirit of cooperation and partnership.
"H, this really isn't working for me, can we figure out a solution that meets both are needs?"
When you do set a boundary, consider ways you might still compromise. For example, with the meal thing, you might have always saved a desert for SS in case he showed up. A quick sandwich for him and a shared desert for all.
If you believe H retailiates, report it to him:
"H, I feel like that is in retaliation for me sticking to my boundary yesterday. I feel hurt and hopeless about improving our life together when that happens. I'm sad and frustrated. I want us each to be able to respect the other's boundaries and still have an active loving partnership."
Go to the meeting. Things that seem impossibly puzzling will become much easier.
