Here's a list of "yoke" verses from the NT:
Take my yoke upon you, and learn from me, for I am gentle and lowly in heart, and you will find rest for your souls.
For my yoke is easy, and my burden is light.”
And another said, ‘I have bought five yoke of oxen, and I go to examine them. Please have me excused.’
Now, therefore, why are you putting God to the test by placing a yoke on the neck of the disciples that neither our fathers nor we have been able to bear?
Do not be unequally yoked with unbelievers. For what partnership has righteousness with lawlessness? Or what fellowship has light with darkness?
For freedom Christ has set us free; stand firm therefore, and do not submit again to a yoke of slavery.
Let all who are under a yoke as bondservants regard their own masters as worthy of all honor, so that the name of God and the teaching may not be reviled.
You can see the need for wisdom. The last verse implies that there are certain yokes in this world that need to be respected. Here, it's a contract of servitude. But it could be marital obligations toward relatives, obligations toward government, etc.
Paul gives some insight in 1Cor 5. He's talking about dealing with a brother in serious unrepented sin. He tells the church to disfellowship the man, and he goes on about their need to be separate from the world and to maintain purity. But then he goes on to give perspective, lest they fall into a carnal extremism:
I wrote to you in my letter not to associate with sexually immoral people—
not at all meaning the sexually immoral of this world, or the greedy and swindlers, or idolaters, since then you would need to go out of the world.
But now I am writing to you not to associate with anyone who bears the name of brother if he is guilty of sexual immorality or greed, or is an idolater, reviler, drunkard, or swindler—not even to eat with such a one.
For what have I to do with judging outsiders? Is it not those inside the church whom you are to judge?
God judges those outside. “Purge the evil person from among you.” -1Cor 5:9-13
We are not the judge of the world, God is. We don’t have to have an abnormal fear of normal intercourse with the world, so long as we maintain our purity before Christ. Our job is to keep ourselves pure, and to be a light; God will deal with the world.
It comes down to us being “in the world but not of it” (Jn 17, Jesus' "high priestly prayer"). There's real freedom in that. We can walk in the newness of life, untainted by the world’s filth, of which there is no lack.
But if some situation is a stumbling block to us, we need to deal with it or avoid it. And wisdom or the leading of the Lord might tell us to stay away from a given situation, sometimes we might not even know exactly why. But even in separation our motives will be right. “To the pure, all things are pure” - Titus 1.
I'm not judging your friend's situation, only giving some guidelines I would use to prove the will of the Lord in such a situation.
