"And there occurred such a sharp disagreement that they separated from one another, and Barnabas took Mark with him and sailed away to Cyprus. But Paul chose Silas and left, being committed by the brethren to the grace of the Lord. And he was traveling through Syria and Cilicia, strengthening the churches." Acts 15:39-41
The truth is that we will not always agree. The bible is our guide in so many ways, but there are many areas that are not specific and are up for interpretation.
In this case, there were two very good friends and brothers in the faith who separated over whether or not to include a young disciple. They both felt so strongly about their polar opposite opinions that they did not continue their work together.
On the face of it, this may seem a tragedy, in reality, however, it is not. You see beloved, the work continued, the number of young "interns" were doubled and separately, the two duos were able to cover more territory and do more work than might otherwise have been possible. Neither of these men who were so strong in the faith and so critical to the growth of the church were dissuaded from the faith because of their difficulties. They continued on.
Some may separate from us due to differences of opinion, but as long as the cause of Christ is served and the spreading of the gospel continues, we must trust that all things are working together for good as part of God's grand design. Let us also not give up hope on maintaining our fellowship one with another. Later, Paul reunited with Mark and described him as being valuable to his work. One way or the other, we will see each other again as long as we remain in Him.