Praise be to Allah
The ayaat you've just recite [Q.S. Al-Ma'idah(5):51] and [Q.S. Ali Imran(3):28] part talks about some problems in the muamala chapter with non-Muslims. The word allies here means that you make them as your brother, family, fight with them, act upon them. If so, then it's clear that it will makes you a murtad. But before we decide if one is murtad or not, we need to know the line of Interraction to a non-Muslims.
One of the principles in aqidah ahlus-sunnah wal jamaah is act of loving or giving wala' (loyality) towards muslim and act of hating, renunciation (bara') towards kafeer and enemies of Islam because of Allah. Take correct action of placing hate or love will strengthen faith of a muslim. Yet on the contrary, wrong action in placing both will result in the destruction of his faith.
Act of interaction to disbelievers:
1. Da‘wah towards them.
It has been narrated on the authority of Abu Mas'ud al-Ansari who said:
من دَلَّ على خيرٍ فله مثلُ أجرِ فاعلِه ...
... One who guides to something good has a reward similar to that of its doer.
(Hadith Sahih Muslim, The Book of Government no. 1893)
2. Don't give salam to them.
Shahih al book parts of Sahih Muslim about greetings. For muslim should not greet non-muslims and if they started it first, just the same to you, not greeting for you too (without salam). (Look for Hadith Muslim no. 2167 and 2163, or al-Bukhari no. 6928)
3. Act of trading is acceptable. Dr. Muhammad Arifin Badri (Lecturer from STDI Imam Syafi'i, Jember, Indonesia) stated:
Even though the Messenger of Allah -peace and prayer of Allah be upon him- managed to conquer the Jews tribes, he still maintained business with them. He entrusted the management of his fields in Khaibar to the jews, with the requirement of profit sharing between them. (Muttafaqun ‘alaihi)
4. Do not love, care, towards non-muslim
Muhammad Shaleh Al-Munajjid rahimatumullah stated:
But acting good and being righteous doesn't mean loving and caring, because love and compassion for unbelievers is not allowed, so should not make it a close friend...
in [Q.S. Al-Mumtahanah(60):8]:
لَّا يَنْهَاكُمُ اللَّهُ عَنِ الَّذِينَ لَمْ يُقَاتِلُوكُمْ فِي الدِّينِ وَلَمْ يُخْرِجُوكُم مِّن دِيَارِكُمْ أَن تَبَرُّوهُمْ وَتُقْسِطُوا إِلَيْهِمْ ۚ إِنَّ اللَّهَ يُحِبُّ الْمُقْسِطِينَ
Allah does not forbid you from those who do not fight you because of religion and do not expel you from your homes - from being righteous toward them and acting justly toward them. Indeed, Allah loves those who act justly.
in [Q.S. Al-Mujadila(58):21]:
لَّا تَجِدُ قَوْمًا يُؤْمِنُونَ بِاللَّهِ وَالْيَوْمِ الْآخِرِ يُوَادُّونَ مَنْ حَادَّ اللَّهَ وَرَسُولَهُ وَلَوْ كَانُوا آبَاءَهُمْ أَوْ أَبْنَاءَهُمْ أَوْ إِخْوَانَهُمْ أَوْ عَشِيرَتَهُمْ ۚ أُولَٰئِكَ كَتَبَ فِي قُلُوبِهِمُ الْإِيمَانَ وَأَيَّدَهُم بِرُوحٍ مِّنْهُ ۖ وَيُدْخِلُهُمْ جَنَّاتٍ تَجْرِي مِن تَحْتِهَا الْأَنْهَارُ خَالِدِينَ فِيهَا ۚ رَضِيَ اللَّهُ عَنْهُمْ وَرَضُوا عَنْهُ ۚ أُولَٰئِكَ حِزْبُ اللَّهِ ۚ أَلَا إِنَّ حِزْبَ اللَّهِ هُمُ الْمُفْلِحُونَ
You will not find a people who believe in Allah and the Last Day having affection for those who oppose Allah and His Messenger, even if they were their fathers or their sons or their brothers or their kindred. Those - He has decreed within their hearts faith and supported them with spirit from Him. And We will admit them to gardens beneath which rivers flow, wherein they abide eternally. Allah is pleased with them, and they are pleased with Him - those are the party of Allah . Unquestionably, the party of Allah - they are the successful.
This clearly states that one should not have love or care to enemies of Allah which also enemies of muslims.
As for a Muslim who interacts with them, with a gentle attitude because they want Islam as their faith, is allowed.
