Matters of Love and War
Both your first two versions seem fine, but the third one does not. As you observe, confession of love is the normal collocation, not *love confession, but it is hard to pin down precisely why that should be so.
It is not so much a matter of grammar but rather one of customary couplings of one word to another. For some combinations, one uses love attributively in front of the noun, but for others, one needs the full prepositional version with love trailing along afterwards.
After all, one has love scenes, love stories, love letters, love bites, love songs, love affairs, love interests, love offerings, and love potions — amongst many others. But one today has only labo(u)r of love not *love labo(u)r (despite Shakespeare’s Love’s Labour’s Lost). This is like how one has affairs of the heart not *heart affairs.
Perhaps this is because when love is used attributively, it may in at least some cases more strongly attract the “about” or “for” notion than the simpler “of” notion. A love story is a story about love. A love potion is a potion for love, not of it.
But that is not a particularly strong tendency, and in some combinations it does not hold.
Really then, given two nouns XXX and YYY in English, whether you can (or must) say the XXX of YYY or the YYY XXX or YYY’s XXX often depends on which version people are most accustomed to hearing and seeing. This can change over time, too.
Besides love, another word whose combinations are not always predictable is war. Consider dogs of war, fog of war, tug of war, prisoners of war, spoils of war, case for war. A war dog would be something else altogether, as would be a war case or a war tug, so we do not say those. With war fog, war spoils, and war prisoners, we just aren’t used to saying them that way. In particular, war fog seems to make no sense at all.
In contrast, we do have war efforts, war crimes, war reporters, war rooms, war dead, and of course war heroes. And we have only crimes of passion, never *passion crimes.
I think your confession of love is like that: that’s how we’re used to hearing it, so that’s what our ear is expecting.
Translation Hazards for Romance Speakers
I notice that your student is calquing Italian assistere in its “attend” or perhaps “join” sense and then dragging along the preposition with it. Neither works well in today’s English.
I’m presuming the desired sense is that Sabina did not so much aid in the confession but rather attended it — that is, she joined them or simply happened to be present to overhear the confession. (Whether the thought was to listen to or to hear or to overhear, well, that’s something else, more related to intent.)
I’ve often heard this very same calquing of this particular verb into English by native speakers of Romance languages with the same verb, whatever its cognate in their respective Latin-derived language. As you note, it doesn’t really carry that “attend” sense in the English — the English of today, that is.
It is quite true that assist could once upon a time do both jobs in English just as it still does in Romance. But these days using it just to mean standing by or being present sounds rather “off” to us. The OED marks three out of the four such senses of assist as obsolete, and the fourth one’s latest citation specifically notes that this is the “French” sense of the verb.
When presenting Shakespeare unedited, this can cause confusion. For example, in The Tempest, this line occurs:
The King, and Prince, at prayers, let’s assist them.
That is not the assist that means aid, but rather the now-obsolete one that meant join them or accompany them. If the word is left unaltered, modern audiences may become confused over its intended sense.
Speaking of dragging the preposition along with it, the choice of arrive to instead of the normal arrive at is also unfortunate, and another sure sign that we’re dealing with a Romance speaker with just one preposition a for situations where English variously uses to or at, plus sometimes in and in less common cases even from.
The Romance learner needs to learn precisely which English preposition a maps to on a case-by-case basis, including those cases where no preposition at all is the best choice. This is just like how the English learner studying Romance must do the same thing going the other direction, for no overarching rule applies. Every verb’s “preposition affinities” are strongly idiomatic and vary from one language to the next.
Best Answer
The problem is that the modifier clause ("Having spent nearly half his life...") refers to one party (the man), while the subject of the sentence is a different party ("we"). To eliminate the dangling modifier, we could rewrite the sentence as:
...so that the modifier clause properly refers to the man rather than to us. But beware of revisions like:
...which commits the same sin: now his grief is the subject of the sentence, and his grief didn't spend half its life by her side, he did.