Er bleibt dem Team treu.

Because treu takes the dative in German when it means loyal or faithful to someone or something.

So the pattern is:

• jemandem treu sein
• jemandem treu bleiben

That is why you get:

• dem Team = dative singular

A few more examples:

• Sie ist ihrem Freund treu.
• Er bleibt seiner Heimat treu.
• Wir bleiben der Marke treu.

For an English speaker, this is worth memorizing as a fixed pattern: treu + dative.

Treu is an adjective.

In this sentence, it is used predicatively, which means it comes after the verb and describes the subject:

• Er ist treu.
• Er bleibt treu.

When German adjectives are used this way, they do not take adjective endings.

Compare:

• ein treuer Freund → adjective before a noun, so it gets an ending
• Der Freund ist treu. → predicate adjective, so no ending

So in Er bleibt dem Team treu, treu stays in its basic form.

Bleiben means to remain or to stay. It focuses on continuing in the same state.

So:

• Er ist dem Team treu. = He is loyal to the team.
• Er bleibt dem Team treu. = He remains loyal to the team.

The second version suggests continuity, often especially when there could have been a change.

For example, if a player had the chance to leave but did not, German often uses bleiben:

• Er bleibt dem Verein treu.

So bleibt adds the idea of staying loyal.

Because it is not directly in front of a noun.

German adjective endings only appear when the adjective comes before a noun, such as:

• ein treues Team
• der treue Spieler

But in Er bleibt dem Team treu, treu is linked to the subject through the verb bleibt, so it is a predicate adjective. Predicate adjectives do not take endings.

This is the same in:

• Sie ist müde.
• Das Wetter bleibt schön.
• Er wird krank.

In this sentence, bleiben works a lot like a linking verb.

A linking verb connects the subject to a description:

• Er ist müde.
• Er bleibt müde.

In the same way:

• Er bleibt dem Team treu.

Here, bleibt links Er with the idea of being treu. The dative phrase dem Team tells you to whom he is loyal.

So bleiben is not describing a physical action here. It is describing a continued state.

German main clauses usually put the finite verb in second position. That gives you:

• Er = first element
• bleibt = second element

After that, the rest of the sentence follows. Here the most natural order is:

• dem Team before treu

So:

• Er bleibt dem Team treu.

That order sounds normal and idiomatic.

You may sometimes see different word orders for emphasis, but this is the standard version. For a learner, it is best to remember the pattern as:

• Subject + bleiben + dative + treu

For example:

• Sie bleibt ihrer Familie treu.
• Der Kunde bleibt der Firma treu.

It can be used with all of those.

In German, treu often means being loyal or faithful not just to a person, but also to:

• a team
• a club
• a company
• a brand
• a tradition
• a principle
• a homeland

Examples:

• Er bleibt seiner Frau treu.
• Sie bleibt dem Verein treu.
• Viele Kunden bleiben der Marke treu.
• Er blieb seinen Überzeugungen treu.

So dem Team treu is a very natural use.

Treu is the normal and very common word here.

It is especially common in phrases like:

• jemandem treu sein
• jemandem treu bleiben

The word loyal also exists in German, but it is used differently and often in more formal or political/business contexts, for example:

• ein loyaler Mitarbeiter
• loyal gegenüber der Firma

For this sentence, treu is much more natural than loyal.

There are a few common options.

Simple past:

• Er blieb dem Team treu.

This is common in written German and news-style writing.

Present perfect:

• Er ist dem Team treu geblieben.

This is very common in spoken German.

Notice that the dative and treu stay the same. Only the verb changes:

• bleibt → present
• blieb → simple past
• ist ... geblieben → present perfect

Yes. Since dem Team is dative, you need a dative pronoun.

For example:

• Er bleibt ihm treu.

Here ihm stands for a masculine or neuter noun in the dative, so it could replace dem Verein, dem Club, or dem Team.

Other possibilities:

• Sie bleibt ihr treu.
• Wir bleiben ihnen treu.

Again, the important thing is to remember that treu goes with the dative.