If I were to choose a bosom friend I would have definitely chosen Abu Bakr as my bosom friend, but he is my brother and my companion and Allah, the Exalted and Gliorious. has taken your brother and companion (meaning Prophet himself) as a friend. (Using translation from Muslim 2383a)
عَنِ النَّبِيِّ ﷺ قَالَ لَوْ كُنْتُ مُتَّخِذًا خَلِيلًا لَاتَّخَذْتُ أَبَا بَكْرٍ خَلِيلًا وَلَكِنْ أَخِي وَصَاحِبِي وَقَدِ اتَّخَذَ اللهُصَاحِبَكُمْ خَلِيلًا