Let us stay under the shades of the following verse from Sura aal-Imran

Believers should not take disbelievers as friends instead of the believers—and whoever does so will have nothing to hope for from Allah—unless it is a precaution against their tyranny. And Allah warns you about Himself. And to Allah is the final return. [3:28]

Muslims should not expose the secrets of Muslims to their enemies. If a Muslims betrays his fellow Muslims and exposes the secrets of Muslims, then he automatically gets out of the circle of Islam. Moreover, Allah declares that He has lifted his shelter from any Muslim who does that. That means in this only-two-club system, Allah is with the Muslims and when a Muslim betrays his fellow Muslims then he is not only leaving the camp of Muslims, actually he is leaving the camp of Allah as well. Allah will not extend his shelter and protection to him. Let the nonbelievers protect him. Let them give him Noble Prize or Knighthood or any other honorary, but these are just temporary worldly honorariums.

this verse coming after the earlier two verses on Allah’s power

This verse in Aal-Imran came after two verses describing the power, majesty and dominion of Allah. These two verses described the supreme qualities that only Allah possess. Hence, our verse today coming after these earlier verses fits very well. How can a sensible person after knowing the dominion and power of Allah still wants to join the club of anti-Allah!

it is okey to behave and say good to others

We need to distinguish between love which is a matter of inner heart feeling and the just treatment and the polite words. A Muslim son or daughter must continue to behave with his nonbeliever parents with just and mercy. He should speak politely with his parents and relatives. However he should not dissolve his identity and compromise on matters of religion no matter how close or dear a person is.

But if they (i.e., parents) pressure you to associate with Me what you have no knowledge of, do not obey them. Still keep their company in this world courteously, and follow the way of those who turn to Me ˹in devotion˺. Then to Me you will ˹all˺ return, and then I will inform you of what you used to do. [Quran 31:15]

A Muslim is never asked to behave rude with a peaceful non-Muslim society which is not at enmity with Muslims.

Allah does not forbid you from dealing kindly and fairly with those who have neither fought nor driven you out of your homes. Surely Allah loves those who are fair. Allah only forbids you from befriending those who have fought you for ˹your˺ faith, driven you out of your homes, or supported ˹others˺ in doing so. And whoever takes them as friends, then it is they who are the ˹true˺ wrongdoers. [Quran 60:8,9]

The companion Abu ad-Darda’ said that when we visited lands of the nonbelievers we apparently smiled on the surface while our hearts used to curse them. Ibn Abbas said, the the taqiyyah (i.e., concealing the hatred while speaking politely) is not what you act and do, it is what you utter by your tongue.

Why we should not love by heart the nonbelievers?

We have seen in verses preceding this verse one reason why we should not take as allies the nonbelievers. When they are asked to take the Quran as a guiding book and a judge they turn away. It would be a crime then to join the club of those who turn away from Quran deliberately and consider as source of guidance books of other philosophers or scholars.

punishments for taking nonbelievers as allies

The greatest punishment of taking nonbelievers as allies is that Allah lifts his protection and makes it a pretext for humiliation and punishment. Here are a list of verses in this regard without comments.

O believers! Do not take disbelievers as allies instead of the believers. Would you like to give Allah solid proof against yourselves? [4:144]

O you who have attained faith, do not take the Jews and the Christians as allies; some of them are allies of one another. And whoever of you allies himself with them is indeed one of them. Indeed, Allah does not guide the unjust people. [5:51]

O you who have attained faith, do not take My enemies and your enemies as guardians, extending love towards them when they have denied what has come to you of the truth, evicting the Messenger and yourselves because you believe in Allah, your Lord—if you have set out to strive in My way and to seek My pleasure. How can you secretly express love towards them while I know better what you have hidden and what you have made public? And whoever of you does that has certainly strayed from the right way. [60:1]

And those who denied— they are guardians of one another. Unless you do this, there will be religious persecution in the land and huge corruption. [8:73]

who choose disbelievers as allies instead of the believers. Do they seek honour and power through that company? Surely all honour and power belongs to Allah. [4:139]

So reading Quranic verses here are the consequence of taking nonbelievers as allies:

Nothing to hope from Allah [3:28]
Allah gets a solid proof against them [4:144]
They become a member of their camp [5:51]
They are the wrongdoers or unjust (Dhalim) [ 5:51]
They are strayed from the right way. [60:1]
Taking nonbelievers as allies cause great religious persecution on earth [8:73]
Taking nonbelievers as allies causes huge corruption on earth [8:73]
They will lose honor and pride and will stay perpetually at the bottom of nations [4:139]

reward for not taking nonbelievers as allies

Those who stay on path and albeit all temptations stick to the camp of believers surely will get great rewards. These reward as just the opposite of the 8 punishments mentioned above. Here is a motivating verse:

You will never find a people who ˹truly˺ believe in Allah and the Last Day loyal to those who defy Allah and His Messenger, even if they were their parents, children, siblings, or extended family. For those ˹believers˺, Allah has instilled faith in their hearts and strengthened them with a spirit from Him. He will admit them into Gardens under which rivers flow, to stay there forever. Allah is pleased with them and they are pleased with Him. They are the party of Allah. Indeed, Allah’s party is bound to succeed. [58:22]

So here is a listing of rewards for those who stay in the camp of Allah:

Allah instaills faith in their heart
Strengthens them with a spirit from Him (i.e., angel Gabriel will be with him)
Admit them to Jannah
Allah becomes pleased with them
They will be pleased with Allah
They are the party of Allah
They are the successful

Allah knows what the heart conceals

Since there are cases when a person can speak politely and act diplomatically with nonbeliever Allah tells us in this verse that what matters is what one conceals in the heart and nobody has access to these intensions except that very person and Allah. It is sufficient that Allah knows about what the heart conceals.