הוא לגמרי בטוח שהפגישה מחר, ואני כבר לא בטוחה בזה.

Because the adjective has to agree with the person it describes.

• הוא is masculine singular, so we get בטוח.
• אני here refers to a female speaker, so we get בטוחה.

This is very common in Hebrew adjectives, especially when they describe a person’s state:

• הוא עייף = he is tired
• היא עייפה = she is tired
• הוא בטוח = he is sure
• היא בטוחה = she is sure

So the change is grammatical agreement, not a change in meaning.

לגמרי means completely, totally, or entirely.

In this sentence, הוא לגמרי בטוח means he is not just sure, but totally sure.

A few similar English equivalents depending on tone are:

• completely sure
• totally sure
• absolutely sure

In everyday Hebrew, לגמרי is very common and often sounds natural and conversational.

Because it is modifying the adjective בטוח.

Hebrew often places adverbs like לגמרי before the adjective or expression they intensify:

• לגמרי בטוח = completely sure
• ממש טוב = really good
• מאוד חשוב = very important

So לגמרי comes right before the word it strengthens.

In Hebrew, the verb to be is usually omitted in the present tense.

So where English says:

• the meeting is tomorrow

Hebrew simply says:

• הפגישה מחר

Literally, this is more like the meeting tomorrow, but grammatically it means the meeting is tomorrow.

This is one of the most important basic patterns in Hebrew:

• הוא עייף = he is tired
• אני בבית = I am at home
• הספר מעניין = the book is interesting
• הפגישה מחר = the meeting is tomorrow

ש־ means that and introduces a subordinate clause.

So:

• הוא בטוח שהפגישה מחר = he is sure that the meeting is tomorrow

This ש־ is extremely common in spoken and written Hebrew. It connects the first idea to the clause that follows.

Compare:

• אני חושב שהוא צודק = I think that he is right
• היא יודעת שאני כאן = she knows that I am here
• הוא בטוח שהפגישה מחר = he is sure that the meeting is tomorrow

In casual speech, sometimes ש־ can sound attached directly to the next word, as it does here.

Usually, no—not in normal standard Hebrew for a sentence like this.

With verbs and expressions like to think, to know, to say, to be sure, Hebrew normally uses ש־ before the clause:

• אני חושב ש...
• היא אומרת ש...
• הוא בטוח ש...

Leaving it out would usually sound unnatural or incomplete.

בזה means about this or about it, and it refers back to the idea just mentioned: שהפגישה מחר.

So:

• ואני כבר לא בטוחה בזה = and I’m no longer sure about that / about it

Hebrew often avoids repeating a full clause if the meaning is already clear.

Notice that with בטוח/בטוחה, Hebrew can work in two common patterns:

1. בטוח ש... = sure that...

   • הוא בטוח שהפגישה מחר

2. בטוח ב... / בטוח בזה = sure about... / sure of it

   • אני לא בטוחה בזה

So the sentence switches naturally from a full clause to a pronoun-like expression.

בזה is made of:

• ב־ = in / on / at / about
• זה = this

Together, in this context, it means about this or about it.

A lot of Hebrew prepositions attach directly to pronouns or demonstratives:

• בו = in him / in it
• בה = in her / in it
• בזה = in this / about this
• על זה = about this / on this

Here, בזה is the natural form after בטוחה.

כבר לא means no longer or not anymore.

So:

• אני כבר לא בטוחה בזה = I am no longer sure about it

This expression is very common in Hebrew and often appears before the word being negated:

• אני כבר לא גר שם = I no longer live there
• הוא כבר לא עובד פה = he doesn’t work here anymore
• אנחנו כבר לא חברים = we are no longer friends

It often suggests a change from an earlier situation. In this sentence, it implies that the speaker used to be sure, but now isn’t.

Because כבר לא functions as a fixed expression meaning no longer / not anymore.

In natural Hebrew, כבר לא stays together:

• אני כבר לא בטוחה
• הוא כבר לא כאן
• הם כבר לא רוצים

Putting לא before כבר would usually sound wrong in this meaning.

So it is best to learn כבר לא as a single unit.

Because הפגישה means the meeting, while פגישה means a meeting.

Since the sentence is talking about a specific meeting that both speakers presumably know about, Hebrew uses the definite article ה־.

• פגישה = a meeting
• הפגישה = the meeting

This is exactly like English:

• He is sure a meeting is tomorrow would sound odd here
• He is sure the meeting is tomorrow sounds natural

In this sentence, מחר functions like a time adverb: tomorrow.

So הפגישה מחר means the meeting is tomorrow.

Hebrew often uses time words directly after the noun phrase without any extra preposition:

• השיעור היום = the class is today
• הטיסה מחר = the flight is tomorrow
• המסיבה בערב = the party is in the evening

So מחר here is not describing the meeting as an adjective; it is saying when it is.

Yes. Hebrew could repeat the clause with ש־ if the speaker wants to be more explicit:

• ואני כבר לא בטוחה שהפגישה מחר

That would mean and I’m no longer sure that the meeting is tomorrow.

The version in your sentence, ואני כבר לא בטוחה בזה, is simply less repetitive and very natural.

So both are possible:

• לא בטוחה בזה = not sure about it
• לא בטוחה שהפגישה מחר = not sure that the meeting is tomorrow

It sounds natural and fairly conversational, but not slangy.

A few things that make it feel everyday and natural:

• לגמרי is common in speech
• כבר לא is very common
• using בזה instead of repeating the whole clause sounds natural and efficient

So this is the kind of sentence you could easily hear in ordinary conversation.