"become manifested when the topic of long-term commitment or marriage arises;"

People might be or stay in a relationship just because they feel guilty because they spent so much time with that person, and don't want to leave even though they have to leave them, just because they were promised to get married, or created a future together already.

"THE POWER OF FAMILIAL ROLES"

The title of this chapter is both dangerous yet helpful, depending on the context. Sometimes, when both sides of the families are supportive, things are easier to handle because the end goal is for them to be united. But, when familial roles are focused more on rivalry, problems, jealousy, aren't built on strong bonds can lead to major conflict, and can affect one's POV on their own relationship. This can be the case when the parents have strong input on their children's lives, thus can affect their relationship with their significant other.

I have seen real life examples of this, where parents got so involved their children's love life, to the extent that they had to call the engagement off because the girls mother was too involved in her love life.

"self-validation are linked that the stage is set for love"

Being seen by someone else's eyes as something more than they are can lead to the feeling of love, which can also boost someone's self-esteem if it is low, thus feeling self-validation and more confident about their appearance.

"“opposites attract” principle but also of the search for subjective ideals."

can refer back to the social psychology theories of attraction, especially the Complementarity theory, showing how partners complete each other when one person is lacking in something, thus them thinking they are the perfect match because they "complete each other". Only I believe that this theory can either break or make a relationship, because sometimes the feeling/longing of wanting to be complete by a person can be a reason for you to depend on you happiness on them, and that is a very dangerous game.

"she loved John and he loved her, wonders what had gone wrong to have caused their parting."

People can acquire an entire relationship based on the the limited knowledge they have the person. Maybe at the beginning this knowledge is strong enough to make the person attracted to another person like the similarity theory going hand in hand with the attitudinal similarity. This can help create a strong bond in the beginning of the relationship (first 3 months), but later, when masks start getting taken off, it might make a difference in the level of attraction and lead to conflict.

"she loved John and he loved her, wonders what had gone wrong to have caused their parting."

this can reflect the idea that some attraction theories proposed, that people can be attracted to each other at the beginning like physical attraction, only for their personalities to not be compatible. I didn't read the book, but this shows that not all relationships workout and that is OKAY.

"In the throes of passion, the adolescent, who reasons that such intensity of feeling must be love, wants to merge with the other in both body and soul,"

I believe that the adolescent years believe in the idea of love, because it is overly romanticise by society, but also because their hormones during that time are very heightened, they tend to feel more intense feelings than in their adult relationships