"Elegy for Jane" certainly addresses Love, but it isn't quite what we might expect. We tend to put this big, complex emotion into three main categories: familial (the love felt between family members), romantic (often including a physical component—yes, we mean sex), and friendship (the love you might feel for a very close friend). So, which category does our speaker's love for Jane belong? Seems kind of tough to squeeze it into any these neat little boxes, which is precisely the problem Roethke wants us to consider.
The speaker doesn't love Jane, he's just a tree-hugger, hung up on nature.
It is impossible to categorize, govern, or explain an emotion as powerful as love. As Emily Dickinson said, "The heart wants what it wants-or else it does not care."