Do Relationships Cause Suffering?

As is the case with millions of others, I am deeply inspired by your words. Thank you for doing what you do! I am struggling with an issue for quite some time and it is a source of endless debate with my friend.

I believe in having deep relationships with other people based on love (with spouse, children, parents, friends etc). My friend argues that humans suffer a great deal when they lose their loved ones to death (e.g., in long term marriages) and that the primary reason for the suffering is due to attachment and dependency. I sense the truth in his words, but I also see great contempt for human relationships in his mind. My argument is that while human relationships are imperfect and usually weighed down by attachment, humans do open up their hearts and are able to connect to each other deeply. There is something really beautiful in this and these relationships teach us valuable lessons and allow us understand ourselves deeply. For example, when I find that I am hating someone, I am often able to trace it back to certain aspect of myself that was unexamined closely before. So I find that relationships actually help me in evolving into a better human being.

I also understand that it is ideal to transcend this individual (or selfish) love to loving all, with the help os spiritual practice. I often experience states of deep love overflowing in my heart, after deep meditation sessions.  So, is there something really wrong in human relationships? Do they need to be shunned and cast away? Do we need to be really careful and vigilant (i.e., policing) for strings of attachment and dependency developing in our hearts? In your opinion, what is the ideal way of seeing/handling human relationships? Can they help us grow?