We are truly saddened to hear about the situation you are facing, and we are here to pray and provide biblical guidance for you. Firstly, we thank God that you have come through cancer. God has a purpose and a plan. God reminds us, For I know the thoughts that I think toward you, says Yahweh, thoughts of peace, and not of evil, to give you hope and a future Jeremiah 29:11 WEB.
We strongly advise you to separate from this relationship and not move in together. It is clear that this person is not positively influencing your life. Remember 1 Corinthians 15:33 WEB tells us, Do not be deceived. Evil companionships corrupt good morals.
Also realize that God does not desire for us to be in close fellowship with those practicing sin. We must love all people and evangelize to those around us, but we should not be intimate with those who practice sin like drug abuse, unless they have been born again and repented from their sins. The Bible tells us in 2 Corinthians 6:14 WEB, Don't be unequally yoked with unbelievers, for what fellowship have righteousness and iniquity? Or what fellowship has light with darkness?
You mentioned that you are living with this person. If this implies any sin, it needs to be addressed. Either way, this seems to be a very unhealthy situation especially with threats and stress involved. 1 Corinthians 6:18 WEB advises, Flee sexual immorality. Every sin that a man does is outside the body, but he who commits sexual immorality sins against his own body.
Concerning the use of drugs, this also is condemned in the scriptures. We are a temple of God and should take care of our body. We are not our own and are bought with a price. We must glorify God by taking care of our body.
Also, we noticed that Jesus was not mentioned or referenced in your prayer request. Remember, For there is one God, and one mediator between God and men, the man Christ Jesus 1 Timothy 2:5 WEB. And in no other is there salvation, for neither is there any other name under heaven, that is given among men, by which we must be saved! Acts 4:12 WEB.
Therefore, we pray for you.
Father, we come before You in the name of Jesus, lifting up our fellow brother/sister who is in a trying situation. We pray for strength, guidance, and wisdom. We pray that You direct according to Your will. Lord, we pray for conviction, repentance, and salvation for this person who is bound by drugs and is being a negative influence. We pray that this unhealthy relationship be broken and used for Your glory. We pray for complete healing from the cancer and any other infirmities. We pray that this situation be worked together for good, being confident that nothing can separate us from the love of God which is in Christ Jesus our Lord Romans 8:28,38,39 WEB. We ask this and thank You for it all in Jesus name.
Lastly, we encourage you to cast all your anxieties on him, because he cares for you 1 Peter 5:7 WEB. And be anxious for nothing, but in everything by prayer and petition with thanksgiving, let your requests be made known to God Philippians 4:6 WEB.