Let's begin by bringing this situation to the Lord in prayer.
Father, we come before You in the name of Jesus Christ, lifting up this man and the woman he is in a relationship with. We pray that You would work in her heart, drawing her closer to You and convicting her of the need to change her lifestyle. We rebuke the spirits of recklessness, indulgence, and immorality that may be influencing her actions, and we command them to leave in Jesus' name. We ask that You would help her to see the importance of spending quality time with her child and the man who cares for her.
Now, let's address the situation with biblical principles in mind. It's clear that there are behaviors present that are not consistent with God's will for our lives. As it is written in 1 Peter 4:3-5 (WEB), "For the time past may be enough for us to have worked the desire of the Gentiles, and to have walked in lusts, drunkenness, orgies, carousings, and abominable idolatries. They think it is strange that you don't run with them into the same excess of riot, blaspheming: but they will give account to him who is ready to judge the living and the dead."
We must remember that God calls us to be holy and set apart. This means that our lifestyles should reflect His goodness and purity. If the woman you are in a relationship with is engaged in behaviors that are not consistent with this calling, it is important to address these issues with her in a loving and compassionate manner.
However, it is also crucial to remember that we cannot change anyone; only God can do that. Our job is to pray for her and to be a godly example in her life and the life of her child. It is also important to examine your own life and ensure that you are walking in a manner that is pleasing to God. Remember, as it is written in Ephesians 5:8-11 (WEB), "For you were once darkness, but are now light in the Lord. Walk as children of light, for the fruit of the Spirit is in all goodness and righteousness and truth, proving what is well pleasing to the Lord. Have no fellowship with the unfruitful works of darkness, but rather even reprove them. For the things which are done by them in secret, it is a shame even to speak of."
Lastly, we want to encourage you to continue praying for this situation, but also to remember the importance of praying in Jesus' name. As it is written in John 14:13-14 (WEB), "Whatever you will ask in my name, that will I do, that the Father may be glorified in the Son. If you will ask anything in my name, I will do it." It is only through Jesus that we have access to the Father, and it is only through His name that we can be saved. If you have not already, consider sharing the good news of the Gospel with the woman you are in a relationship with, and encourage her to place her faith in Jesus.
How you treat her and her child will be a great witness for Jesus Christ. Make sure you are treating her with compassion and love.