The other, for phenomenologists, comes about through a process of analogy. I look at the other and realise that the other can look back at me, so that every way that I understand them is equally a way that I can be understood by them. Add to this a certain hunger, that the subject is searching in experience for something that will fill an inner void and you have the ingredients of a theory of relations. The primacy of subjectivity is retained even if this subjectivity is an inherently anxious one. The very nature of the subject might be seen to include an element of storm and stress, but it remains stably positioned at the origin of experience. A relational phenomenon like 'falling in love' is as much a secondary structure here, a sort of bad faith, as it is in evolutionary psychology where it serves as a particular relational or communicational or social technology with its own affordances. Consider on the contrary the possibility that loving is a  fundamental attribute of subjectivity, rather in the way that anxiety is for the existentialists. In this alternative take, it is anxiety as the possibility of the loss of love that is secondary. This explains as many things as the other, it would seem, and it also would give more credence to the psychoanalysis, since you could say that we are born into the state of being in love and the first drama of life is the learning to relinquish it.