De când a primit rapelul, câinele este bine.

Here de când means since, in the sense of from the time when.

So:

• De când a primit rapelul = Since he/it received the booster

Romanian uses de când both:

• in statements: since
• in questions: since when?

You can tell which meaning it has from the sentence structure and intonation.

A primit is the perfectul compus (the Romanian compound past), which is one of the main ways to talk about a completed past action.

It is made of:

• the auxiliary a = has
• the past participle primit = received

So a primit literally corresponds to has received, but in many contexts it is best translated as simple past received.

In this sentence, it refers to the completed event of getting the booster.

Because the sentence describes a state that started after a past event and is still true now.

• a primit = the dog got the booster at some point in the past
• este bine = the dog is well now

This is very similar to English Since he got the booster, the dog has been well / is well. Romanian often uses the present tense in the main clause to show that the result still continues.

Rapelul means the booster or the booster shot, especially in a medical or vaccination context.

It comes from rapel = booster / follow-up dose.

The ending -ul means the, so:

• rapel = booster
• rapelul = the booster

Because Romanian usually puts the definite article at the end of the noun, not before it.

So:

• câine = dog
• câinele = the dog

This is one of the big differences from English. Instead of a separate word like the, Romanian often attaches the article to the noun.

The subject is understood from context: it is the dog.

Romanian often leaves out subject pronouns or even an explicit subject when it is clear who is being talked about. So:

• De când a primit rapelul, câinele este bine.

is understood as:

• Since the dog received the booster, the dog is well.

Romanian avoids repeating the noun if the meaning is already clear.

Because bine and bun are used differently.

• bine = well / fine
• bun = good

When talking about someone’s condition or health, Romanian normally uses bine:

• Câinele este bine = The dog is fine / well

If you said câinele este bun, that would usually mean the dog is good in the sense of behavior, quality, or character, not health.

Yes. In everyday Romanian, e is a very common short form of este.

So these mean the same thing:

• Câinele este bine.
• Câinele e bine.

Este is slightly more formal or careful in style, while e is very common in normal speech.

Yes, it is normal to use a comma here because the sentence begins with a subordinate clause:

• De când a primit rapelul, câinele este bine.

The comma separates:

• the time clause: De când a primit rapelul
• the main clause: câinele este bine

This is similar to English, where a comma is also often used when a dependent clause comes first.

Yes. Romanian allows some flexibility. You could also say:

• Câinele este bine de când a primit rapelul.

This still means basically the same thing: The dog has been well since it received the booster.

The version with De când... first puts more emphasis on the time relationship. The version with Câinele este bine... first puts more emphasis on the dog’s condition.

Yes. That is one reason learners sometimes find it confusing.

Compare:

• De când a primit rapelul, câinele este bine.
  = Since it received the booster, the dog is well.

• De când este bine câinele?
  = Since when is the dog well?

So de când can mean either:

• since
• since when

The rest of the sentence tells you which one it is.

Yes, very possibly.

• Câinele este bine = The dog is fine / okay
• Câinele se simte bine = The dog feels well

Both are natural, but there is a slight difference:

• este bine focuses on the dog’s overall condition
• se simte bine focuses more on how the dog feels

In many contexts, either one would work.