"How to develop composure?"

Focus on yourself. Maybe this will seem wrong to someone, but in our situation we will have to show not the best qualities. One of them is selfishness. It must be taken as a principle that you owe nothing to anyone. This is completely your life and you decide what, how and when to do it. There are basic values - love, work, family and friends, and the rest - problems, circumstances, ill-wishers, emotions - just garbage, it needs to be thrown away. This will allow you to take life into your own hands and begin to manage it yourself.