The most convincing expression of the self-sacrifice for someone else would be the claim: ‘I am nothing else than you’.
But the claim is logically impossible. When you are nothing, your sacrifice does not matter. Then, when you pretend to be or to live for somebody else, you deny the reality of the two distinct bodies. Thus, you posit your sacrifice in a spiritual domain which does not matter, too.
Therefore, the sexual love as one of the strongest forms of love between humans indulges itself in many illogical acts which involve the two partners. The detachment from those acts (especially of sexual nature) may start the improper but logical investigation about the value of the self-sacrifice. And nobody can see it at his or her partner.
[Since the relation between parents and children does not benefit from the same great amount of illogical acts, it is accordingly oftener affected by logical adversities which drive to a total separation. They often begin by questioning the value of the mutual sacrifice. It is a surprising separation, since it is a natural bound and thus apparently stronger than sexual love.]