We understand your concern and the frustration you feel when it seems like victories and defeats are evenly split in your life. First, let's address the misconception that there might be an agreement between God and the devil. The Bible clearly teaches that God is sovereign and the devil is a fallen angel who seeks to steal, kill, and destroy John 10:10. There is no agreement between them; rather, there is a spiritual battle taking place.
In Ephesians 6:12 WEB it says, For our wrestling is not against flesh and blood, but against the principalities, against the powers, against the world's rulers of the darkness of this age, and against the spiritual forces of wickedness in the heavenly places.
It's important to remember that God allows trials and tribulations to refine our faith and draw us closer to Him. In James 1:2-4 WEB Consider it nothing but joy, my brothers, when you fall into various temptations, knowing that the testing of your faith produces endurance. Let endurance have its perfect work, that you may be perfect and complete, lacking in nothing.
Moreover, we must understand that our struggles are not always a result of a battle between God and the devil, but often a result of our own choices and the consequences of living in a fallen world. Our actions, as well as the actions of others, can lead to both victories and defeats.
Regarding your observation about healings and deaths, it's crucial to remember that God's ways are higher than our ways, and His thoughts higher than our thoughts. Isaiah 55:8-9 WEB For my thoughts are not your thoughts, neither are your ways my ways, says Yahweh. For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts.
God has a divine right to heal or not heal. He sees the whole picture and does not do things based on our limited understanding or desires. It is okay though to ask for healing and expect it because of faith in scripture.
Let's pray together:
Dear Heavenly Father,
We come before You in the name of Jesus Christ lifting up our brother/sister who is feeling frustrated and confused. Lord, we ask that You give them the wisdom and understanding to see that You are in control and that Your ways are perfect. Help them to trust in You and Your divine plan for their life and the life of others. Deliver them from the evil one when they are being tempted or tested. Comfort them in their trials and help them to grow stronger in faith and closer to You at the end of them.
In Jesus' name, we pray. Amen.
Lastly, we want to encourage you to continue trusting in God, even when things don't make sense. Keep praying and seeking His face. Ensure you are praying specifically in the name of Jesus Christ. It is only by the name of Jesus that we have access to God. And, there is no other name by which we can be saved.
Prayer Focus: God, Thank You for loving me. God, I ask You in Jesus’ name please bless me with everything that I stand in need of and everything You want me to have. 
