Pakistan has not actively helped kill American troops. Yes it has supported the Taliban at its inception and as a party during its rule, but then dropped support after 9/11. You can go on about 'clandestine' help and so called 'support' all you want but that's politics for you, and something which the US has also actively engaged i.e. supporting dubious groups in order to achieve objectives, for example the Contra Rebels.
The US did help S.Vietnam but once losses started to mount and the war became unpopular they left. As for standing by allies yes it did in its early years, as in the Second World War and immediately the post war era, but in the modern era its support has wavered for countries as time has gone on, or come at a cost. The S.Koreans were perturbed at Trump's overtures so decided to make a big for peace themselves, the other example of Japan has them hosting a massive US military presence, something you would balk at. As for Taiwan, even with threats of Chinese invasion the US support has remain muted. The allies they do stand by are closely linked by culture, race and faith e.g. the UK, Canada, Australia and so on. You have Israel as well, due to a large part to the immensely successful Jewish lobby, and the contribution Jewish people have made to the US.
India doesn't come under any of these criteria and headings, and has literally been stamped as a 'counter' to China, a shaky and what many would describe loose link for any alliance. Spare us the whole 'we are the biggest democracy' speech as well, it's about what you can do for them, and their commitment to any conflict that could break out between China v India is questionable, how do you think hey will sell that to their public? They could provide material support but again this is a big IF, and with the odds massively stacked again you v China this could very well end up with an outcome not dissimilar to the what the Vietnam war.
Let's see the latest news;
NEW DELHI: India has decided to raise import tariffs on 29 goods from the US after having deferred retaliatory higher duties multiple times since announcing them in June last year, said people with knowledge of the matter.
India has also taken the US to the World Trade Organization (WTO) dispute settlement mechanism over the imposition of import duties on steel and aluminium.
//economictimes.indiatimes.com/articleshow/69796585.cms?utm_source=contentofinterest&utm_medium=text&utm_campaign=cppst
This must be the beautiful relationship you write about.