Who is happy ?

 Earlier in (5:22) Krishna has said that "Pleasures concieved in the world of senses have a beginning and end and give birth to misery (Easwaran).."

and because they have a beginning and an end but are ,in a way, addictive, they have no end till the end(death) .
Sri Sankaracharya's  explanations of desire,anger and implulse and how to identify them are very apt .

शक्नोतीहैव यः सोढुं प्राक्शरीरविमोक्षणात्।
कामक्रोधोद्भवं वेगं स युक्तः स सुखी नरः।।5.23।।

śaknōtīhaiva yaḥ sōḍhuṅ prākśarīravimōkṣaṇāt.

kāmakrōdhōdbhavaṅ vēgaṅ sa yuktaḥ sa sukhī naraḥ..5.23

English translation by Swami Sivananda

5.23 He who is able, while still here (in this world) to withstand, before the liberation from the body, the impulse born out of desire and anger -- he is a Yogi, he is a happy man. 

English translation by Swami Gambhirananda (on Sri Sankaracharya's Sanskrit Commentary) 5.23
yaḥ śaknōtī , one who can, is able to;
sōḍhuṅ, withstand;
iha eva, here itself, while alive;
prāk, before;
śarīravimōkṣaṇāt, departing from the body, till death-. Death is put as a limit because the impulse of desire and anger is certanily inevitable for a living person. For this impulse has got infinite sources. One should not relax until his death. That is the idea.
Kama, desire, is the hankering, thirst, with regard to a coveted object-of an earlier experience, and which is a source of pleasure-when it comes within the range of the senses, or is heard of or remembered.
And krodha, anger, is that repulsion one has against what are adverse to oneself and are sources of sorrow, when they are seen, heard of or remembered. That impulse (vēgaṅ) which has those desire and anger as its source (udbhava) is kāmakrōdhōdbhavaṅ vēgaṅ. The impulse arising from desire is a kind of mental agitation, and has the signs of horripilation, joyful eyes, face, etc. The impulse of anger has the signs of trembling of body, perspiration, bitting of lips, red eyes, etc. He who is able to withstand that impulse arising from desire and anger,
sah narah, that man; is
yuktah, a yogi; and
sukhi, is happy, in this world.

5:24 deal with What kind of a person, being established in Brahman, attains Brahman?

Arjuna said :Forgive me Lord for calling you a friend

Having seen the Divine form of Krishna in its full splendour, Arjuna, thought about the times when they were growing up and playing together.

सखेति मत्वा प्रसभं यदुक्तं , हे कृष्ण हे यादव हे सखेति।

अजानता महिमानं तवेदं , मया प्रमादात्प्रणयेन वापि।।11.41।।

sakhēti matvā prasabhaṅ yaduktaṅ

hē kṛṣṇa hē yādava hē sakhēti.

ajānatā mahimānaṅ tavēdaṅ

mayā pramādātpraṇayēna vāpi..11.41..
 

English translation by Swami Sivananda

11.41 Whatever I have presumptuously said from carelessness or love, addressing Thee as O Krishna! O Yadava! O Friend! regarding Thee merely as a friend, unknowing of this, Thy greatness.  

prasabhaṅ, rashly, slightingly; 

pramādāt through inadvertence, being in a distracted state of mind; 

vāpi, or even; 

praṇayēna , out of intimacy-itimacy is the familiarity arising out of love; whatever I have said because of that reason;

यच्चावहासार्थमसत्कृतोऽसि , विहारशय्यासनभोजनेषु।

एकोऽथवाप्यच्युत तत्समक्षं , तत्क्षामये त्वामहमप्रमेयम्।।11.42।।

yaccāvahāsārthamasatkṛtō.si

vihāraśayyāsanabhōjanēṣu.

ēkō.thavāpyacyuta tatsamakṣaṅ

tatkṣāmayē tvāmahamapramēyam..11.42

English translation by Swami Sivananda
11.42 In whatever way I may have insulted Thee for the sake of fun, while at play, reposing, sitting or at meals, when alone (with Thee), O Krishna, or in company -- that I implore Thee, immeasurable one, to forgive.