Executive Order 13780 (the final version of the "Muslim ban" or "travel ban"), as amended by Presidential Proclamation 9983 from February 21, 2020, suspended the entry of Nigerian nationals as immigrants. However, multiple federal court injunctions (including from the Supreme Court) blocked the various travel bans from affecting immigrants with a "bona fide relationship" to a U.S. person. What exactly constituted a "bona fide relationship" was somewhat vague, but a spousal or fiance relationship meets any reasonable definition. After all, you have to, quite literally, prove a bona fide relationship exists before a K-1 visa is issued.
This is just somewhat-informed speculation on my part, but I would say: it is possible, but not certain, that Trump tries another iteration of the travel ban. He talked about it to some extent during his most recent campaign, but it was much less prominent than during his 2016 campaign. So, it may happen, but it's by no means a foregone conclusion. If it does happen, just like last time, federal court injunctions would almost certainly exempt immigrants with a bona fide relationship to a U.S. citizen. Even still, such a situation would inevitably cause significant uncertainty, stress, and financial costs in the form of attorney's fees.
I'm sorry that this is something you have to worry about now, and I hope for your sake, and for the sake of everyone else in your position, that this won't be an issue.