It is possible, but unlikely that what he is saying is true. I don't know federal investigation procedures to comment if it is at least plausible. I don't believe that they would ever advise that he break it off from you unless you were a target, especially not for such flimsy reasons. They certainly do not give a crap about facebook likes unless it is a post talking about terrorism or some such thing. It is very unlikely this is real.

I have gone through somewhat similar things, 100% certain that the police would be banging on my door at any time. I could not tell you why they would but I completely believed it. It could be something similar with your boyfriend, just more elaborate.

As to how to deal with it, I have little insight. But if he is saying that the #1 concern of his psychiatrist, real or imagined, is suicide and is thinking that some unlikely intervention will save him - not too likely as I think the government would move to have him committed on the basis of him being a danger while he is investigated, just my intuition if the investigation is actually real - I think it is at the point where you are more than justified in filing a police report and see if they will interview him to see if a civil commitment is necessary.

At this point, I think confronting him would be pointless in the best case and very scary in the worst. I don't say this lightly, and it is possible my own experiences are misjudging it but it seems the safest path for all.

Good luck and stay safe.