I would really appreciate if someone could help me with this. I don't know how to prevent the second phrase from not breaking at the end of the line. Surely, I can break the phrase on my own (third phrase), but then it doesn't fit the whole width of the text and I have to make it fit manually. I need Latex to take care of that line break. Apparently, the reason is contour package, but I do need its very bold font.
EDIT: I simplified my code. Sorry about that.
\documentclass[10pt]{article}
\usepackage[usenames]{color}
\usepackage[outline]{contour}
\definecolor{MIR}{RGB}{187, 30, 16}
\contourlength{0.3pt}
\contournumber{20}
\newcommand{\MIR}[1]{\contour{MIR}{#1}}
\begin{document}
I only need some text width enough to prove my point, so I'll write some nonsenses.
\MIR{I only need some text width enough to prove my point, so I'll write some nonsenses.}
\MIR{I only need some text width enough to prove my point, so I'll write}\linebreak \MIR{some nonsenses.}
\end{document}

soulpackage and the\ulmacro. Hence, you could (should?) probably simplify your minimum working example further by leaving out all\ul-related directives and not loading thesoulpackage. – Mico Jan 30 '18 at 05:40