Perhaps the most important thing I can tell you is to urge you not to give up on your friends. Someday they may realize their own spiritual emptiness and hopelessness, and give their lives to Christ.
After all, no one is completely beyond God's reach. Although they don't believe in God right now, He still loves them, and yearns for them to turn to Him in repentance and faith. The Bible says that God "is patient ... not wanting anyone to perish, but everyone to come to repentance" (2 Peter 3:9). Are you praying for them, and are you asking God to help you be a witness to them both by the way you live and by your words?
You are right about heaven: Heaven truly will be a place of supreme happiness and peace. And one reason it will be so wonderful is that we will be with Christ. As the Bible says, "And so we will be with the Lord forever" (1 Thessalonians 4:17). All the loneliness and heartache we feel in this life will be over, because our lives will be filled with the joy of His presence.
Although the Bible doesn't answer all our questions about heaven, you can be sure that you will experience the reality of Christ's peace. You also will realize the justice and perfection of His ways. But in the meantime, make it your goal to live for Christ, and to share the message of His love with others.