Your original goal was commendable: to help this young man get his feet on the ground during a difficult time in his life. The Bible tells us to "Share with God's people who are in need. Practice hospitality" (Romans 12:13).
And your goal after two years have gone by should be exactly the same: to help him get his feet on the ground. In other words, you should seek what is best for him and sitting around the house all day isn't what is best. By allowing this to go on, you are hurting both him and yourselves. Unless he has some type of physical or emotional problem that keeps him from working, the time has come for him to get a job and move into the real world.
I suggest you sit down and talk frankly with him about his future. You might even ask him when he thinks he will get a job and then set a deadline for moving, and stick with it. If he has contact with his parents, seek their support for what you are doing. Let your nephew know you love him but because you love him, you care what happens to him. The Bible bluntly says, "If a man will not work, he shall not eat" (2 Thessalonians 3:10).
Above all, urge him to give his life to Jesus Christ, and then to seek God's will for his future. God loves him, and He has a perfect plan for his life. God may not show it to us all at once but all we need to know is the next step.