Love-making & force of contrast?

"But as Lombard pointed out the various features of the scene to his companion, I fear that his chief motive was less an admiration of Nature that sought sympathy than a selfish delight in making her eyes flash, seeing the color come and go in her cheeks, and hearing her charming unstudied exclamations of pleasure,—a delight not unmingled with complacency in associating himself in her mind with emotions of delight and admiration.
It is appalling, the extent to which spoony young people make the admiration of Nature in her grandest forms a mere sauce to their love-making.
The roar of Niagara has been notoriously utilized as a cover to unlimited osculation, and Adolphus looks up at the sky-cleaving peak of Mont Blanc only to look down at Angelina’s countenance with a more vivid appreciation of its superior attractions.
It was delicious, Lombard thought, sitting there with her on the rear platform, out of sight and sound of everybody.
He had such a pleasant sense of proprietorship in her!
How agreeable—flatteringly so, in fact—she had been all day!
There was nothing like traveling together to make people intimate.
It was clear that she understood his intentions very well: indeed, how could she help it?
He had always said that a fellow had shown himself a bungler at love-making if he were not practically assured of the result before he came to the point of the declaration.
The sensation of leaving everything else so rapidly behind that people have when sitting on the rear platform of a train of cars makes them feel, by force of contrast, nearer to each other and more identified."
- Deserted

In the last two paragraphs, what do "love-making" and "by force of contrast" mean? Courting? Contrast with what?