Was there really a burden on Prophet’s chest ?
No because Qur’an says
مَا أَنزَلْنَا عَلَيْكَ الْقُرْآنَ لِتَشْقَى
20:2 We have not bestowed upon you this Qur’an to cause you any hardship.
إِلَّا تَذْكِرَةً لِّمَن يَخْشَى
20:3 But, only as a reminder to those who fear (faltering in their journey of life).
[Badar wrote: “Haven’t I laid open, revealed and disclosed all to you? You turned away, shunned and forsook it, and distanced yourself, considering it weak or incorrect.”]
Pls have a close look of 9:40 which gives a totally different picture form what you stated above . ‘Grieve not .God with us ‘ this statement came in an extremely difficult situation and needless to say that without having a firm believe in the correctness of the message such a statement could not be made .
إِلاَّ تَنصُرُوهُ فَقَدْ نَصَرَهُ اللّهُ إِذْ أَخْرَجَهُ الَّذِينَ كَفَرُواْ ثَانِيَ اثْنَيْنِ إِذْ هُمَا فِي الْغَارِ إِذْ يَقُولُ لِصَاحِبِهِ لاَ تَحْزَنْ إِنَّ اللّهَ مَعَنَا فَأَنزَلَ اللّهُ سَكِينَتَهُ عَلَيْهِ وَأَيَّدَهُ بِجُنُودٍ لَّمْ تَرَوْهَا وَجَعَلَ كَلِمَةَ الَّذِينَ كَفَرُواْ السُّفْلَى وَكَلِمَةُ اللّهِ هِيَ الْعُلْيَا وَاللّهُ عَزِيزٌ حَكِيمٌ
9:40 If you do not help the Messenger, God will help him, as always. When the disbelievers drove him out of his home, they were just two men. They had to seek refuge in a cave. The Messenger said to his companion, “Grieve not. God is with us.” Then God sent His reassuring peace upon him, and supported him with invisible forces of faith and courage (9:26). He made the word of the disbelievers utterly low. God’s Word remains Supreme, for God is Mighty, Wise.
41:42 No falsehood can ever approach it openly or in stealth, in the past, present or future, a revelation from all Wise, Owner of praise.