: What to do when you get stuck trying to connect sentences? At first I blamed coffee (I thought caffeine had a chemical which blocked "editing" skills). But then I realized it happens to me

Agree with John Smithers. You do not have to necessarily connect them. Keep it simple and trust what you have written. A couple of suggestions on the particular text of yours:

This lack of fervor didn't bother Eri, though. As far as she was concerned, not all couples needed to be crazy in the bedroom.
This lack of fervor didn't bother Eri, though. She knew that not all couples needed to be crazy in the bedroom.
This lack of fervor didn't bother Eri, though. (Most) certainly not all couples needed to be crazy in the bedroom.

However the best (according to me is):

This lack of fervor didn't bother Eri, though. Not all couples needed to be crazy in the bedroom.

For the second one:

The kind of sex she had with Takeshi was just fine.
For herself, the sex she had with Takeshi was just fine.
Sex, the kind she had with Takeshi, was just fine.
For Eri, the kind she had with Takeshi was just fine.

However, your original

The kind she had with Takeshi was just fine.

seems just fine to me.
Some tips:

Try not to focus on connecting the sentences. What you have written is just fine. If you strain too hard to try to connect the sentences, there may be repetitive elements that may come in.

Analyze and see if the sentences make sense. Both individually and in context. As long as they do, you need not try and connect them. Your readers get what you want to say. The sentences stand individually. Should work for you.

If you are feeling compelled to connect your sentence, try and see if there is a way you can modify the second sentence slightly which will not change the meaning but will make the structure clearer. In that case, you will not be compelled to connect them.

Words and phrases like "Certainly", "As far as he/she...", "Although...", "In spite of....", "though, by all means..." etc. can be used depending on the text and the meaning you want to convey but you may end up overusing them which would not be nice.

Try and keep such usage to minimum. In my opinion as long as the sentences flow freely and the meaning is in place, you should not bother about connecting them. An occasional usage of connectors is fine to avoid bumps in sentences.

Try not to blame coffee!

Hope it helps! Cheers!

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Don't connect them. That's it.
Really, you are rewriting here. The most important part of rewriting is to compare the rewrite with the original version. If you have any doubt that the rewrite is improvement, don't change anything. And I guess you already tried some rewrites.
If you want to change something, you can also consider using punctuation marks instead of words:

This lack of fervor didn't bother Eri, though; not all couples needed to be crazy in the bedroom.
This lack of fervor didn't bother Eri, though--not all couples needed to be crazy in the bedroom.

But that's just fine also:

This lack of fervor didn't bother Eri, though. Not all couples needed to be crazy in the bedroom.

In the second case you just can replace "kind" with "sex":

Not all couples needed to be crazy in the bedroom. The sex she had with Takeshi was just fine.

Don't make it overly complicated. If in doubt, trust your creative voice. That's the one which wrote the first version.

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