This is a recurring issue with narrow columns. It is less critical when you have wider columns because you can stuff more words in a line and excess space can be spread more smoothly between words.
The only solution I see to mitigate the problem is to allow hyphenation.
Unfortunately your document (only this sample I hope) is totally direct formatted: everything is Default Paragraph Style and every emphasis (bold, font face, etc.) is manually applied. You won’t go far before being confronted to formatting dead ends.
Learn how to use styles. Read the Writer Guide for an introduction. Practice on scratch documents before tackling your goal.
Enabling hyphenation is done in the Text Flow tab of the style definition.
Presently, if you do it on Default Paragraph Style, it will be enabled for all your document, including locations where it should not. This is so because everything (except the header) is assigned the same paragraph style. Bulk discourse should be styled Text Body. Headings should receive Heading n depending on the level of the heading. There are many others and you can define your own (for comment, note, remark, … paragraphs).
Intra-paragraph formatting is done with character styles (such as Strong Emphasis for bold, Emphasis for italics) instead of applying manually the attribute (I know, Word does it this way because it does not know about styles and their semantics).
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