The speaker imagines himself as an old man in some rundown place, remembering a single rainy night and the person who shared it with him. He is caught between two feelings. One moment he insists he will be young again, the next he admits that despair, age and "doom" are waiting to pull him under. The line "This is the last chance. / This is not the last chance." shows how unsteady his hope is.
The poem keeps shifting between present and future. Right now there is a small, ordinary scene: a room, a lover at the sink pinching their face in the mirror. Yet he is already mourning it, certain that time will wash the joy away like a river and that the other person will leave. The mood is wistful, anxious and quietly desperate. The last lines, with candles burning in strange windows "to mark my fame," read as bitterly ironic: the only recognition he pictures is lonely grief.