I'm pretty sure he is the guy who showed up at the end of the chapter (name's slightly different then the spoilers), but he's only the ML if you think a fiance who hates your guts and calls you evil from day 1 is the ML(and he only get's worse), so no i don't believe he is, not entirely sure who the ml is but i know it's not him since i skimmed the spoilers because i was curious about the description (if you've read villainess level 99, imagine if the heroine from that story was engaged to eumellia, except switching the characters to the first prince and the MC, that's how insane the prince is).
As for if he's trouble or is a nuisance, he's trouble, i think he even tries to get a inquisition against her at one point.