לא הבחנתי בכתם על החולצה עד שחזרתי הביתה.

The ending ־תי marks first-person singular past tense in Hebrew: I.

So:

• הבחנתי = I noticed / I discerned
• חזרתי = I returned / I came back

A useful point: in the first person, Hebrew does not distinguish masculine and feminine in the past tense. A man and a woman would both say הבחנתי and חזרתי.

Hebrew does not use English-style do-support.

In English, you say I did not notice.
In Hebrew, you simply put לא before the verb:

• הבחנתי = I noticed
• לא הבחנתי = I didn’t notice

So לא is the normal way to negate a past-tense verb here.

Because the verb להבחין often takes the preposition ב־ when it means to notice / to discern.

So Hebrew structure is:

• להבחין ב... = to notice ...

That means the thing noticed is introduced by ב־, not by את.

So:

• הבחנתי בכתם = I noticed the stain

This is just how this verb works in Hebrew. It is a common verb-preposition pattern that learners need to memorize.

This is because the preposition ב־ often combines with the definite article ה־.

So:

• ב + הכתם becomes בכתם

In unpointed modern Hebrew spelling, the ה is not written separately after ב־.

That means בכתם can represent:

• be-ketem = in/at a stain or a stain
• ba-ketem = in/at the stain or, with this verb, the stain

In this sentence, context tells you it means the stain.

Without vowel marks, you usually know from context.

Here, the sentence is naturally understood as the stain, not just a stain. That is especially likely because:

• the meaning of the sentence points to a specific stain on a specific shirt
• להבחין ב־ often refers to noticing some particular thing in context

So although the spelling is the same, the intended reading here is ba-ketem = the stain.

על means on, especially on the surface of something.

A stain is typically on a shirt, so:

• כתם על החולצה = a stain on the shirt

Using בחולצה would more naturally suggest in the shirt or something less standard here. For a visible mark on the surface, על is the normal choice.

Also notice an important grammar difference:

• ב־, כ־, and ל־ can merge with ה־
• על does not merge with ה־

So you get:

• בכתם from ב + הכתם
• but על החולצה, not a merged form

עד ש־ is a very common way to say until before a full clause.

So:

• עד = until / up to
• עד שחזרתי = until I returned

The ש־ is attached to the next word in writing, so שחזרתי is just ש־ + חזרתי.

A useful comparison:

• עד הערב = until evening
• עד שחזרתי הביתה = until I returned home

So when Hebrew follows until with a whole verb clause, עד ש־ is very common.

הביתה means home / homeward, with a sense of movement toward home.

The final ־ה is an old directional ending, sometimes called the directional heh. It often appears in words of motion.

So:

• חזרתי הביתה = I returned home
• אני בבית = I am at home

That difference is important:

• הביתה = motion toward home
• בבית = location at home / in the house

This is why חזרתי הביתה is the natural form here.

Not exactly.

• ראיתי = I saw
• הבחנתי = I noticed / I became aware of / I discerned

You can see something with your eyes without really noticing it.
This sentence emphasizes that the speaker only became aware of the stain later, so הבחנתי is a better fit than ראיתי.

In other words, הבחנתי is about awareness, not just vision.

The given order is very natural and neutral:

• לא הבחנתי בכתם על החולצה עד שחזרתי הביתה

But Hebrew word order is fairly flexible, so you could also say:

• עד שחזרתי הביתה, לא הבחנתי בכתם על החולצה

That version puts more emphasis on the time frame first. The basic meaning stays the same.

So the original sentence is normal, but it is not the only possible word order.