The meaning of this sentence is: A pot of old wine is a new love, half melancholy and half warm.
One explanation is: the "new love" in the poem refers to new wine, and old wine represents a long time, implying that people's lives are long and they will always encounter unsatisfactory things. Maybe this is The normal state of life, everyone should have an open mind, so that they can appreciate the beauty of life. There is no need to be melancholy or sad about this. What is supposed to come will always come. What is supposed to go will always go. Half drunk and half awake. Just treat it.
Another explanation is: this poem expresses that life is impermanent and that you don’t need to take everything too seriously, just treat it half drunk and half awake.