How to parse this sentence ending in は

Question

I encountered this sentence which I'm not able to parse/read (in bold):

また恋愛中の相手の恋人に、本の話など仕掛けてはいけない。たとえば遊園地に行って黙って恋人とジェットコースターに乗って遊ぶことに比べたら、ずっと不毛な喋りに過ぎないからだ。 だが同じ本を読むことでも、同じ本の話でもいいからやってみた方がいい。もしも恋愛が峠を越えたと思えたり、これは失敗だったと思えたりしたときには。

The first part can be translated as:

もしも恋愛が峠を越えたと思えたり → If you think that your relationship is going through a difficult part

But then, I don't know what これは is referring to and what is the meaning of ときには at the end of the sentence. My translation for that part would be something like "in times in which you think that this (the relationship?) failed".

Answer 1

Judging from the surrounding context here, the last part means:

だが同じ本を読むことでも、同じ本の話でもいいからやってみた方がいい。もしも恋愛が峠を越えたと思えたり、これは失敗だったと思えたりしたときには。

However, even if it's the same book, reading it, or even just talking about it with your partner, is worth trying — if and when you have felt your current romantic relationship was past its prime or was a failure.

• This おなじ本 is hard to interpret without the previous context, but the gist is "A book is not worth reading or talking about when you are deeply in love, but the same book can be worth reading or talking about (in certain situations)".
• This 峠を越えた seems to be used negatively ("past its prime"). Usually 盛りを過ぎた or something should be better.
• もしも～ときには modifies the previous sentence like a subordinate clause. Adding this clause in a separate sentence as an afterthought has made this part tricky and interesting. The は at the end is just a topic marker, which indicates ときに is the topic of the previous sentence.
• これは失敗だった is "This (relationship) ended in failure".

Basically the whole passage is saying something like this: "Books can't make your current relationship a success, nor can they undo your mistake you have already made. But they can help you relive your heartbreak and therefore help you in the future. So at the end of your relationship, you should read romance stories and share your thoughts with your partner you are thinking of parting with".

Answer 2

The logic in this passage is not in the best of shape, that's for sure (aka there's some degree of babbling). But I do sense the overall sentiment in the passage. Here is my translation:

People in the early stages of a romantic relationship should not have conversations about books. That's because unlike getting on a roller coaster together where you don't have to say anything, you're just stuck forever in small-talk land. But even if it's just about a book you've both read, you should go ahead and try to make conversation if you've got absolutely nothing else. For instance, do it if you feel you've gone past the climax in your relationship, or when you feel like you just ruined the date with a mistake.

And here's how I would clean up the logic in the Japanese:

まだ恋愛中の恋人に、本の話など仕掛けてはいけない。そういう話でずっと不毛な喋りをするよりは、遊園地に行って黙って恋人とジェットコースターに乗ったほうがましだ。 だが本当に話に困っているときは、同じ本の話でもいいからやってみた方がいい。たとえば、恋愛が峠を越えたと思った時や、失敗しちゃったと思ったときにとか。

In terms of what the "これは" means, it actually does not refer to any specific matter. It's used to express some inner dialogue of the speaker, like "Oh shit I just screwed this one up". "this one" = これは