Relationships. It's very helpful to know that there are Four Qualities which, if the couple share, the relationship will get on very well together. If one person has a lot of one of these qualities, and the other person has a little bit, the relationship won't work so well.
The four qualities are: Generosity, Morality, Wisdom, and a Pali word, Saddha, which means confidence or faith. I'll explain them in brief:
Generosity is very easy to understand. What if one person in a relationship has a lot of Generosity, and the other is very stingy? Is that relationship going to work? No.
Morality, again obvious. If one person keeps good morality and the other person wants to go off with every person they meet behind their partner's back is the relationship going to work? No, of course not.
Wisdom, what if one person is very wise and smart and the other is kind of dumb. They are going to miss a sharing there. There's always going to be a teacher-student relationship rather than a friend-friend relationship. So, if wisdom is too high in one and the other person doesn't have much, whether it's spiritual wisdom or normal wisdom, it's going to be difficult. There's always one person leading the other, it's not a "sharing" relationship.
Now, Saddha or faith, this can include a religious spiritual practice that people are following. It can include, simply, the confidence in techniques and methods. On the religious level, if one person is a Christian and one person is a Muslim and they have an intimate relationship, it's going to be hard. We've seen it. Maybe a few of them can do it, but it's really hard. The reason it's very hard is they are not sharing on a very important level in their lives. If I go to the temple and someone else is going to the mosque, and every Sunday we go different ways, we're not sharing something that's so very important, so it makes it difficult.
Now even if a couple have the same spiritual practice as far as religion goes, what if someone has strong confidence and faith in a particular teacher but the other person doesn't? Again, we have the same sort of mix here, that you're gong to miss communication on certain levels, and communication is one of the most important aspects of a relationship. If you don't have good communication, it's going to be hard.
Now the other part of the question, "How do we guard against our attachment to our partner becoming unbeneficial? How do unselfish emotions help with this?"
That's just it, the unselfish emotions are what helps with this. Develop more Compassion for your partner. You don't want to be attached to them just for what you want. Develop more Lovingkindness for your partner. This helps us to see them as human beings, see them as an individual. Someone who's sharing your life, sharing a journey, but they're not yours to hold on to, to keep. They're not yours. That sort of attachment you can't have. Whether you want to or not, you simply can't have it. It's against the truth, the facts of life. Impermanence is the facts. Dukkha are the facts.
So with a negative, unbeneficial attachment, we can break that quite a bit with opening our heart, with Compassionate/Lovingkindness, Sympathetic Joy and Equanimity to our partner. Seeing them as a human being. Hoping they can grow and work, and hoping that you can share life together in a good way.
Back to the beginning, that's how you can support each other and not hinder each other in the practice.