I'm touching several topics in this wall. First, why can't we simply enjoy the company of others without trust, and with the expectation that it will end at any time. Second, why is love worth the heartbreak? Third, why do people never blame love itself?
First, why is a trust based, long-term commitment of love good?
People, generally speaking, like stability. It's why we make commitments. Commitment is good for society, and without it we wouldn't be able to make plans. I think it's difficult for people to "just enjoy the company of people" because if you do that without expecting them to stick around, you're living on the edge of chaos.
How can I run a business if I don't trust that my employees will show up for work? How can I play tennis on Thursdays if I don't trust the other club members to be there? How can a child survive if her parents aren't committed to feeding her?
The feelings of love, are there to help bind us to our commitments.
Really, "love" is too broad a term, so let's be more specific and look at romantic relationships e.g. marriage.
Traditionally, your marriage should be the most stable relationship you have in your life. It is a commitment between two people to support each other emotionally, to raise children together, to share finances, and live domestically. This is highly beneficial, as it makes it so you don't have to worry about as much stuff, because you can divide the labour between two people. I watch the kids, while she gets groceries. She pays the bills while I'm at work, she massages my back, after I make supper etc. Marriage is a serious commitment, the kind of commitment you don't make with just anybody.
Marriage, and indeed love in many other forms, is an exceptionally practical thing. It might be fair to speculate that humans evolved to seek out a love relationship because having a stable family is just so practical. Some research suggests married couples live longer, which might be because of the practical benefits of stability and splitting the work, thus reducing stress and increasing productivity.
If you want to live without marriage or "love" then go right ahead, but if that research is true than life will probably be harder.
As for heart break...well it makes sense. Because marriage is so practical, losing that relationship will make life harder, so we don't want to do that. Sure you can find another relationship, but that takes time and effort, and it means having to build another relationship. As an analogy, I will be sad if my house burns down because all the time and money I spent in building and filling the house is gone, and I must start again. Sure, there's opportunity there as well, but it doesn't lessen the loss.
Feeling negative emotions isn't a bad thing either, it's part of what makes us human, and avoiding love because you want to avoid pain is honestly absurd.
As for "why is it never love's fault?"
Well love isn't a thing. You can't go out in the world and find love, because love doesn't exist without people. Love is an adjective that can be used to succinctly describe two peoples feelings towards each other, and those feelings they have are a result of their actions. People make love (whether sexual or not) through their actions. If a marriage falls apart it's because one person stops loving the other, not because Cupid decided to go get his arrows.