A couple of thoughts and scripture references:
Church does not get between us and Jesus, it unites us to him and each other.
**He is before all things, and in him all things hold together. He is the head of the body, the church. He is the beginning, the firstborn from the dead, that in all things he himself might be preeminent. (Col 1:17-18)
And he put all things beneath his feet and gave him as head over all things to the church, which is his body, the fullness of the one who fills all things in every way. (Eph 1:22-23)
And he gave some as apostles, others as prophets, others as evangelists, others as pastors and teachers, to equip the holy ones for the work of ministry, for building up the body of Christ, until we all attain to the unity of faith and knowledge of the Son of God, to mature manhood, to the extent of the full stature of Christ, so that we may no longer be infants, tossed by waves and swept along by every wind of teaching arising from human trickery, from their cunning in the interests of deceitful scheming. (4:11-14)**
This is a visable unity that is being talked about, not just individuals.
**You are the light of the world. A city set on a mountain cannot be hidden. (Mt 5:14)
But he knew what they were thinking and said to them, "Every kingdom divided against itself will be laid waste, and no town or house divided against itself will stand. (Mt 12:25; Mk 3:25; Lk 1:17)
I pray not only for them, but also for those who will believe in me through their word, so that they may all be one, as you, Father, are in me and I in you, that they also may be in us, that the world may believe that you sent me. (Jn 17:20-21)**
The unity of the Church is a sign that He was sent by God and it bears witness to Him and the reality of who He is and what He came to do for us.
Maybe you could try using some shock tactics and ask why he feels the need to be seperated, unless you don’t think a confrontational approach is appropriate.
**May the God of endurance and encouragement grant you to think in harmony with one another, in keeping with Christ Jesus, that with one accord you may with one voice glorify the God and Father of our Lord Jesus Christ. (Rom 15:5-6)
Greet one another with a holy kiss. All the churches of Christ greet you. I urge you, brothers, to watch out for those who create dissensions and obstacles, in opposition to the teaching that you learned; avoid them. For such people do not serve our Lord Christ but their own appetites, and by fair and flattering speech they deceive the hearts of the innocent. (Rom 16:16-18)
For the time will come when people will not tolerate sound doctrine but, following their own desires and insatiable curiosity, will accumulate teachers and will stop listening to the truth and will be diverted to myths. (2 Tim 4:3-4)
If he does not listen, take one or two others along with you, so that ‘every fact may be established on the testimony of two or three witnesses.’ If he refuses to listen to them, tell the church. If he refuses to listen even to the church, then treat him as you would a Gentile or a tax collector. (Mt 18:16-17)**
I hope that is helpful.