Affects are transindividual, if that helps — they may pass through subjects, but they’re situated fundamentally in a pre-individual “milieu” or context/environment. Consider the specificity involved in a certain degree of heat — heat transfers between bodies, at rates related to the bodies interface to each other. The radiation of intensive degrees passes through the entire field; it doesn’t belong to subjects, though they may participate in the dissipation or intensification.
But even speeds are also this way: pure celerities which activate bodies. Thought is an extensive fluid medium of which each individual has a tiny “flux” which seems to belong to them, but which pre-exists and extends beyond them. Simondon is the key reference here on the problem of the pre-individual and trans-individual (as opposed to the “merely” inter-individual...)
Another quick thought here might be about the molecularity of affects: the way they participate only in an indirect and statistical way in the construction of molar properties (like the emotive flux of sentient bodies.) Their primordial reality, where they have full existence, is the pre-individual field of intensities, from which individuals emerge and fall back. (A glorious body without organs...) There are links here to Spinozism and substance-monism that might be interesting to pursue: the perfect innocence of becoming and affects as movements rather than subjects, operating pre-individual intensities on a differential plane. Affects transdifferentiate bodies; are “learning” or “healing” emotions, exactly? Do they really belong to you the way your joy or sadness do?
Deleuze is the key reference in my mind, though again it is effectively a Spinozist-Nietzschean concept “maximized” by Simondonian analyses of the pre-individual, inter-individual, trans-individual, etc. —Klossowski might be another jumping off point, who shows how some feelings participate in movements which tend to dissolve or “forget” the individual identity.