The speaker has been falling asleep hugging a pillow, and she opens by pushing back on the idea that this feels like holding someone you love. It doesn't, and she lists why: no familiar smell, no touch of skin, no heartbeat. The pillow can't give anything back. The poem's real subject is the absence of a particular person, and the pillow only makes that absence easier to see.
The turn comes when she says "you as well," which suggests she is speaking to someone who does the same thing. She then argues that going to sleep with someone on your mind is worse than sleeping beside the wrong person. The ending is quiet and a little defeated: "For now, you're a pillow. / And that's enough / Just for me to sleep." The mood is lonely and tender, with a dry, conversational humor that keeps it from becoming melodramatic. She doesn't pretend the substitute works. She just admits she'll take it.