Теперь мне не так досадно вспоминать этот день, потому что к ночи мы не только объяснились, но и по-настоящему помирились.

Because досадно here is being used in an impersonal construction.

Russian often expresses feelings like this with:

• a word such as трудно, приятно, грустно, обидно, досадно
• plus the person experiencing the feeling in the dative case

So:

• мне досадно = I feel upset / It is upsetting to me
• literally, something like to me, it is upsetting

You would not normally say я досадный here, because досадный is an adjective meaning something more like annoying / vexing, and it describes a noun, not the experiencer's feeling.

So:

• Мне досадно вспоминать этот день = It upsets me to remember that day

Досадно means something like:

• upsetting
• painful in an annoyed or regretful way
• vexing
• it bothers me

In this sentence, it suggests emotional discomfort mixed with regret or hurt. It is not as strong as deep grief, and not as simple as ordinary annoyance. In context, мне не так досадно вспоминать этот день means:

• it is not so painful/upsetting for me to remember that day now
• remembering that day no longer bothers me as much

Here так means so or to such a degree.

So:

• досадно = upsetting
• так досадно = so upsetting / upsetting to such a degree
• не так досадно = not so upsetting / not as upsetting

This is a very common pattern in Russian:

• не так трудно = not so difficult
• не так важно = not so important
• не так страшно = not so scary

In this sentence, теперь and не так work together:

• Теперь мне не так досадно... = Now it is not so upsetting for me...

It is in the infinitive because it depends on the impersonal predicate мне не так досадно.

Russian often uses this pattern:

• Мне трудно понять
• Ему приятно видеть
• Нам странно слышать
• Мне досадно вспоминать

So the infinitive expresses the action that causes the feeling.

It is imperfective (вспоминать, not вспомнить) because the meaning is general: to remember / to think back on that day. It refers to the act of recalling it, not to a single completed moment of remembering.

Compare:

• вспоминать = to remember, to recall, to be thinking back on
• вспомнить = to remember suddenly, to recall successfully at one moment

Here the idea is: it is upsetting to remember that day, so imperfective is natural.

Because вспоминать takes a direct object in the accusative case.

So:

• этот день is accusative singular masculine
• for an inanimate masculine noun like день, the accusative looks the same as the nominative

Examples:

• вспоминать день
• вспоминать встречу
• вспоминать друзей

In this sentence:

• вспоминать этот день = to remember that day

К ночи means by nightfall, toward night, or by the time night came.

It suggests a change completed by a certain point in time.

So:

• к ночи = by evening / by night / by nighttime
• ночью = at night, during the night

That is an important difference.

Compare:

• К ночи мы устали = By nightfall we were tired.
• Ночью мы разговаривали = We talked at night.

In your sentence:

• потому что к ночи мы... = because by nightfall we...

It marks the time by which the reconciliation had happened.

Yes. It is related to объяснить / объяснять, but объясниться has a special meaning.

Объясниться often means:

• to explain oneself
• to talk things through
• to have it out
• to clear things up between people

So мы объяснились does not just mean we explained. It means something more like:

• we talked things out
• we clarified things between us

This is why it fits well before помирились:

• first they explained themselves / cleared things up
• then they reconciled

The ending -ся / -сь often makes a verb reflexive, but in Russian reflexive verbs do not always mean literal self-action. They can also express:

• action directed back to the participants
• mutual action
• a change of state
• an idiomatic meaning that differs from the non-reflexive verb

Here:

• объясниться = to explain oneself / to talk things out
• помириться = to make peace / reconcile

In context, both are effectively mutual:

• мы объяснились = we had an explanation with each other / we talked things through
• мы помирились = we reconciled

So the -сь is essential; these are standard dictionary forms with their own meanings.

Because the subject is мы = we.

In Russian past tense, verbs agree in:

• gender for singular
• number for plural

So:

• я помирился / помирилась
• он помирился
• она помирилась
• мы помирились

Since мы is plural, both verbs take the plural past ending:

• объяснились
• помирились

This is a very common paired structure meaning not only ..., but also ...

So:

• не только объяснились, но и по-настоящему помирились = not only talked things through, but also truly reconciled

This structure emphasizes that the second action goes further than the first.

A few examples:

• Он не только позвонил, но и приехал. = He not only called, but also came over.
• Мы не только обсудили проблему, но и решили её. = We not only discussed the problem, but also solved it.

In your sentence, the logic is:

1. they spoke and cleared things up
2. more importantly, they really made peace

По-настоящему means:

• truly
• really
• genuinely
• for real

So:

• помирились = reconciled
• по-настоящему помирились = truly/genuinely reconciled

It adds emphasis: this was not just a formal or temporary peace. They really made up.

This matters because объяснились and помирились are close in meaning but not identical. You can talk things through without fully restoring the relationship. По-настоящему makes it clear that the reconciliation was real.

Russian word order is flexible, and the beginning of the sentence often highlights the most important frame for the statement.

Starting with теперь emphasizes the contrast between now and before:

• Теперь мне не так досадно... = Now it doesn't upset me as much...

This makes sense because the second half explains why things are different now:

• because by nightfall we had talked things through and truly reconciled

You could move words around, but this order sounds natural and focused:

1. теперь sets the time frame
2. мне не так досадно gives the emotional state
3. вспоминать этот день names what causes that feeling

Because the sentence refers to a completed result.

• мириться = to be making peace, to reconcile, to make up
• помириться = to reconcile successfully, to make up completely

Likewise:

• объясняться = to be talking things through
• объясниться = to have the clarifying talk and complete it

The phrase к ночи also supports perfective verbs, because it points to what had been achieved by nightfall.

So:

• к ночи мы не только объяснились, но и по-настоящему помирились means that by that time, both actions had been completed.

It sounds reflective and slightly literary or emotionally nuanced.

A few features create that tone:

• досадно is more nuanced than a simple everyday word like плохо
• к ночи sounds a bit more narrative than plain вечером
• не только..., но и... gives a carefully structured contrast
• по-настоящему помирились adds emotional depth

So the sentence feels like someone looking back on a difficult day and saying that it has become easier to remember because the conflict ended well.