Perhaps -- Continuously Thinking About Another Person Has It's Place for Reproductive Purposes

A one-track mind, maybe part of Nature's survival mechanism in relationship to hyper-focusing on someone to reproduce with. Kind of like the "honeymoon stage" when being in-love is part of the bonding for a full-bloomed romance, the one-track-mindness that happens when someone is romantically courting another, may be a very essential part of the desire to romantically bond for reproductive purposes and the survival mechanism for human beings, because (perhaps) the hyper-focus allows one of another person's desire, to be the focus of attraction for reproductive purposes. (And not necessarily the focus, related to an OCD condition.)

Trisha Yearwood sings "Thinkin' About You" -- which is a song, about an individual's continuous thoughts about another person.