يفهم صديقي هذا الشعور.

Because Arabic often uses verb-first word order in ordinary statements. This sentence is a very common pattern:

verb + subject + object

So:

يفهم = understands
صديقي = my friend
هذا الشعور = this feeling

You can also say صديقي يفهم هذا الشعور. That is also correct, but it puts a little more focus on my friend.

يفهم is the imperfect (non-past) form of the verb فَهِمَ = to understand.

Here it means he understands or, depending on context, he is understanding. In simple sentences like this, English usually translates it as the simple present: understands.

The يـ at the beginning is the marker for third person masculine singular in this form.

Arabic verbs already include information about the subject, such as person, gender, and number. So يفهم by itself already tells you he understands.

But it does not tell you who he is. Adding صديقي identifies the subject clearly:

يفهم = he understands
يفهم صديقي = my friend understands

So the noun is not redundant; it tells you exactly who the he is.

It is made of:

صديق = friend
ـي = my

So:

صديقي = my friend

This ـي is a attached possessive pronoun suffix. English uses a separate word (my), but Arabic often attaches it directly to the noun.

Because a noun with a possessive suffix is already definite.

So:

صديق = a friend / friend
الصديق = the friend
صديقي = my friend

Once you add ـي (my), you do not also use الـ. In other words, my friend is already specific, so the is unnecessary.

In standard Arabic, when a demonstrative like هذا (this) directly modifies a noun, that noun is usually definite, so it normally takes الـ.

So the normal pattern is:

هذا + definite noun

That gives:

هذا الشعور = this feeling

If you say هذا شعور, it would usually be understood differently, more like this is a feeling, not this feeling.

Because شعور is a masculine singular noun, and هذا is the masculine singular demonstrative meaning this.

So:

هذا = this (masculine singular)
هذه = this (feminine singular)

Since شعور is masculine, هذا الشعور is correct.

Although it is written الشعور, it is pronounced ash-shuʿūr, not al-shuʿūr.

That is because ش is a sun letter. With sun letters, the ل of الـ is not pronounced; instead, the following consonant is doubled in pronunciation.

So:

Written: الشعور
Pronounced: ash-shuʿūr

This is a pronunciation rule only; the spelling stays the same.

It is the direct object of the verb يفهم.

The action is understanding, and the thing being understood is this feeling.

So the structure is:

يفهم = verb
صديقي = subject
هذا الشعور = direct object

In full grammatical analysis, the object is in the accusative case, but in normal Arabic writing the case endings are usually not shown.

Yes. That is completely correct.

Both are natural:

يفهم صديقي هذا الشعور
صديقي يفهم هذا الشعور

The first is a typical verbal sentence with verb-first order.
The second is more subject-first, which can sound slightly more emphatic or topic-oriented.

For a beginner, it is useful to recognize both patterns as normal Arabic.

It can cover more than one present-time idea, depending on context. The Arabic imperfect can express things like:

• he understands
• he is understanding
• he does understand

In a simple sentence like this one, the most natural English translation is usually understands. Arabic does not need a separate word like English does or a special form like is understanding unless the context requires it.