When is it love? When is it attachment? I have this misunderstanding about love and attachment as they relate to one another. It's hard to put in words, so I'll try with some examples first.

My understanding is that love is something you give away without expecting anything in return. While love where you need or want something from the other person (like for example, expect that other person to make you happy, or you want to control the other person in some way, or try to change them to be more of how you would want them to be, etc) is actually attachment.

One example of true love I can think of is love for your children. You love them unconditionally. You understand they are their own person, with their own dreams, aspiration, thoughts, etc, so whatever they do, good or bad, you support them, help them, etc. You don't try to change them, or influence them, or impose your ideas on them, or have them accomplish the things you couldn't (e.g. I couldn't go to med school, but my child will), etc. No matter what happens, you love them because they are your children, and you love them no matter what they do.

Taking that further, even in the presence of death, I still can understand love (at least I think I do). Everyone dies. Your children might die. And even if you love them and will miss them if they are gone, or suffer after they are gone, that suffering doesn't linger. You continue to love your children even after they are gone (or at least the idea of them or the memory of them).

But here is another example. You love your partner. You think you love them like in the example above. But then they cheat on you with some other person. If you loved your partner unconditionally, you would be OK with that... I think. If being with someone else makes them happy, you should be happy for them, right? But in most relationships, you expect from your partner that they don't cheat on you, or to behave in a certain way. When that expectation is broken, you suffer. Arguments start, resentment, maybe violence towards that person. Is this because of attachment to the person and not love? Because we expect them, and demand, that they behave in a way that doesn't hurt us or make us suffer, that we are attached to the idea that your partner is only ours to have?

So I guess, my question is this: What is love and what is attachment in a relation with your partner? What happens to love and attachment when they cheat with someone else? (for most of the people I know, death is less painful than being cheated upon; suffering caused by death eventually heals, but being cheated upon lingers for much longer).

Can you truly love someone with no attachment so that no matter what they do, you do not end up suffering?
When is it love?
There's Buddhist doctrine about the brahmaviharas which are three different kinds of love ...

I hope you're well
I don't want to hurt you
I rejoice in your virtue/success

... plus equanimity as the fourth.
If you loved your partner unconditionally, you would be OK with that
In the old days before &quot;no-fault divorce&quot; people (in Anglophone countries) used to sue each other for adultery: and the alleged &quot;damage&quot; used to include Alienation of affections.
I think the theory was that if your partner was adulterous then you'd be receiving less affection from them -- an affection which should have been, as their spouse, rightfully yours.
And I think that contradicts your premise, i.e.

My understanding is that love is something you give away without expecting anything in return.

I think another Buddhist theme is that, you do things because they (actions/intentions) are morally right or virtuous. Conversely you don't do things just because you feel like it (e.g. presumably shouldn't hurt people if or because you feel angry).
Because we expect them, and demand, that they behave in a way that doesn't hurt us or make us suffer, that we are attached to the idea that your partner is only yours to have?
I guess that -- expecting behaviour -- might work if you can form a contract, have a meeting of minds, with a sane and reliable partner.
Conversely some people (sometimes children) don't like conforming to other people's expectations.
With such a one, unreliable, a possible winning strategy might be (I don't know if this is applicable to you, feasible, or Buddhist -- but based on experience) if they ask e.g., &quot;What do you expect me to do here?&quot;, reply, &quot;I don't expect you to do anything. You can do...&quot;
Then provide a safe environment, where they can't easily hurt themselves. And the necessities of life. And age-appropriate toys or tools. And good friends, some enjoyable group/social activities -- role models.
I think that behaviour/misbehaviour is partly conditioned/dependent -- if somebody is seeking some liberation then perhaps it's wise to ensure their environment is moral, safe, sane, unoppressive and with opportunities for them to be or to become good friends themselves.
Can you truly love someone with no attachment so that no matter what they do, you do not end up suffering?
I think so if you're semi-enlightened.
You suggested already that you can have children without their causing your suffering.
If I know children, they'll transgress in various ways, large or small -- and you're probably supposed to interact with them and correct their behaviour -- maybe without stopping-loving them though.
There's some doctrine here about choosing a spouse or partner, for what that's worth -- preferably one who is equal.
I think that a or the key to &quot;not suffering&quot; is to behave ethically. There's a sutta Kimattha Sutta: What is the Purpose? (AN 11.1) which begins ...

I have heard that on one occasion the Blessed One was staying near Savatthi in Jeta's Grove, Anathapindika's monastery. Then Ven. Ananda went to the Blessed One and on arrival, having bowed down to him, sat to one side. As he was sitting there he said to the Blessed One: &quot;What is the purpose of skillful virtues? What is their reward?&quot;
&quot;Skillful virtues have freedom from remorse as their purpose, Ananda, and freedom from remorse as their reward.&quot;
&quot;And what is the purpose of freedom from remorse? What is its reward?&quot;
&quot;Freedom from remorse has joy as its purpose, joy as its reward.&quot;
&quot;And what is the purpose of joy? What is its reward?&quot;
&quot;Joy has etc.

I equate that &quot;freedom from remorse&quot; with non-suffering -- &quot;I do not regret it&quot;.
See for example Sīlānussati
In context I think that an example of sīlānussati might be Akkosa Sutta: Insult (SN 7.2) where the buddha seems to be happy.
In my experience that happiness might be in retrospect, i.e. good behaviour now leads to &quot;joy&quot; later.
See also What is the basis?