"And then I'm thinking - is it so impossible to imagine or believe?" reflects a moment of introspection and doubt about love and happiness. The speaker questions whether it's truly unrealistic for a man and a woman to experience happiness together, even if only for a short time.
The quote suggests that fleeting happiness is all that many people have in life. It emphasizes the transient nature of joy in relationships and the human desire to believe in the possibility of shared happiness, even amidst life's uncertainties.