For starters, Luis Muñoz Marín was more pro-autonomy than he was pro-independence. That being said, he did affiliate himself with the pro-independence Liberal Party and worked with them during the late 1920s and earl 1930s. When the great Depression hit, the Liberal Party toned down their pro-independence stance significantly (after all, doesn't really make sense to advocate for independence while the world is plunged into economic ruin). By this time, the only party being vocal Independence was the Nationalist Party but their methods were different from the Liberal Party and the Puerto Rican Independence Party. Luis Munoz Marin joined the Liberal Party and became senator. By this time, the Liberal Party was more focused on handling the economic depression and improving public institutions than achieving independence. Luis Munoz Marin and Rexford Tugwell are credited with having PR included in the New Deal which led to an influx of federal funding to improve the island's infrastructure. Fast forward a couple of years, Senator Millard Tydings proposed a bill that would give PR independence which had the support of most Major Parties on the island. It did not, however, have Luis Munoz Marin's support as he saw it as a way to set Puerto Rico up for economic failure. As a result, he was expelled from the Liberal Party and would later give him space to found the PPD party which focused on bringing progress to rural areas. From there he continued to push for a series a big economic reforms collectively known as "Operation Bootstrap" as part of this economic vision, a close relationship with the US was desirable and thus, in 1952, he pushed for Estado Libre Asociado (ELA) which gave PR autonomy over its domestic affairs (which helped ensure Puerto Rican culture remained intact) while reaping the economic benefits of being in a union with the US. At the time, it was seen as the best of both worlds and had broad support.

As for the opium claim, none of his biographers, or contemporary accounts, support Denis' claim. It has no strong basis. The claim that he was still an addict even as Governor is even less plausible. Many actual historians in the UPR have cast serious doubt on this claim. As for the FBI report, like many FBI reports done under Hoover, were simply false. As the book points out, the FBI also looked into Pedro Albizu Campos and his files are also full of rumors that were simply false. In short, Denis' book in the UPR is considered a work of historical fiction that seeks to paint a narrative. Denis is not a historian nor is he held to the standard of one. If you really want to learn about PR history, you should read anything and everything from Fernando Pico, an actual historian of much renown in PR and Latin America.