Learn Hardcore German: Ich verliere ständig meinen Schlüsselbund, deshalb hängt er jetzt am Haken. - I am constantly losing my key ring, therefore it is hanging on the hook now.

Ich verliere is present tense and can express a repeated/habitual action, especially with ständig (constantly/all the time): “I keep losing…”.

Ich verlor = simple past (“I lost…”) and sounds more like a single past event; also less common in everyday speech for this kind of statement.
Ich habe verloren = present perfect (“I have lost…”) and would usually refer to a specific earlier time or result, not a general habit.

What exactly does ständig mean here, and where does it normally go in the sentence?

ständig means constantly / all the time / repeatedly. In neutral word order it often sits near the verb or after it:

Ich verliere ständig meinen Schlüsselbund. (very natural)
You could also front it for emphasis (Ständig verliere ich…), but that’s more stylistic.

Why is it meinen Schlüsselbund (accusative)? How do I know the case?

The verb verlieren takes a direct object (what is being lost), so it requires accusative.
Schlüsselbund is masculine (der Schlüsselbund), so in accusative it becomes:

mein → meinen (masculine accusative ending -en)
Thus: meinen Schlüsselbund.

What is the difference between Schlüssel, Schlüsselbund, and Schlüsselring?

der Schlüssel = a key
der Schlüsselbund = a bunch/bundle of keys (keys together as a set)
der Schlüsselring = the key ring (the metal ring itself; sometimes used loosely like “keychain”)
In everyday German, Schlüsselbund is very common for “my keys / my bunch of keys”.

Why is it deshalb and not weil? What’s the grammar difference?

deshalb is an adverb meaning therefore/that’s why, and it connects two main clauses. So the second part stays a main clause with verb in position 2:

…, deshalb hängt er jetzt am Haken. (verb hängt is 2nd)

With weil (“because”), you typically create a subordinate clause where the verb goes to the end:

…, weil er jetzt am Haken hängt.
Both are fine; deshalb emphasizes the result (“therefore…”), while weil emphasizes the reason (“because…”).

Why is there a comma before deshalb?

Here the comma separates two independent clauses (two main clauses). In German, it’s standard to use a comma between main clauses when they’re linked in this kind of way, especially in writing:

Ich verliere …, deshalb hängt …
You may also see it as two sentences: Ich verliere … . Deshalb hängt … .

Why is it hängt er and not er hängt after deshalb?

In German main clauses, the finite verb is normally in position 2 (the “V2 rule”). If deshalb is placed first, it occupies position 1, so the verb must come next:

Deshalb (pos. 1) hängt (pos. 2) er …
If you started with er, you’d get: Er hängt jetzt am Haken. That would be fine too; it just doesn’t put deshalb first.

What does jetzt add here? Is it literal “now” or more like “from now on”?

It often implies a change of situation: now (as a consequence / these days / from now on) it’s kept there. In context it can mean:

“So now it’s hanging on the hook (instead of being left elsewhere).”
German jetzt can be literal “right now,” but here it commonly suggests “as of now / currently.”

Why is it am Haken and not auf dem Haken?

am = an dem (a contraction) and an is the usual preposition for something hanging on a hook (attached to it):

am Haken hängen = “to hang on the hook”
auf dem Haken would sound less natural because auf is more like “on top of” a surface.

Why is Haken dative here? How do I know an takes dative?

an is a “two-way” preposition (an + accusative or an + dative).

dative when describing location/state (where something is)
accusative when describing movement/direction (where it’s going)

Here it’s a location/state: it is hanging (not being moved):

(wo?) am Haken → dative
If you describe putting it there:
Ich hänge ihn an den Haken. (wohin? → accusative)

What does hängen mean here, and how is it different from hängen lassen or aufhängen?

hängen (intransitive) = “to hang” (be in a hanging state): Der Schlüsselbund hängt am Haken.
hängen (transitive) = “to hang something”: Ich hänge den Schlüsselbund an den Haken.
aufhängen often stresses the action of hanging something up: Ich hänge den Schlüsselbund auf. / … an den Haken auf.
hängen lassen = “to let something hang” (often different contexts, e.g., clothes, arms; also figurative).

Why is it er (he) for the keyring? Isn’t that weird?

German pronouns follow grammatical gender, not natural gender. der Schlüsselbund is masculine, so you refer back to it with er:

der Schlüsselbund → er
Even for objects, er/sie/es is normal in German.

Could I replace deshalb with darum, deswegen, or also? Any difference?

Yes, common alternatives are:

darum / deswegen / deshalb = “therefore / that’s why” (very similar; deswegen and deshalb are extremely common)
also = “so / therefore” but more conversational and can sound like a spoken transition
All would keep main-clause word order: …, deswegen hängt er jetzt am Haken.

Can I say Ich verliere ständig meine Schlüssel instead?

Yes. That would mean “I keep losing my keys” (plural) rather than “my bunch of keys.”

meine Schlüssel = plural accusative (because der Schlüssel → plural die Schlüssel)
Both are idiomatic; Schlüsselbund highlights them as a set.

Is the sentence implying someone else put it on the hook, or that I did?

The given sentence with hängt er jetzt am Haken describes the resulting state (“it’s now hanging…”), without saying who did it.
If you want to state you did it, you’d typically say:

… deshalb hänge ich ihn jetzt an den Haken. (action, accusative)
or
… deshalb habe ich ihn jetzt an den Haken gehängt. (completed action)