I would assume that from a 2022 perspective, parts of the book (towards the end, not using any spoilers) could be seen as homophobic, but I get what the author was doing and in context he was making a statement about nonconformism and parallel changes with his experience coming back from Vietnam War.
As a side, I generally struggle with the idea that one should judge historical perspectives by today's standards - and 'Forever War' (haven't read the other books in the series) has aged comparatively well given the fact that it was written almost 50 years ago.