Have you noticed when you meet a particular brother or sister for the first time, you get along with them instantly. You agree on most things, you feel comfortable in their presence and most importantly you talk to them as if you have known them for years.
The Prophet (sallallahu alayhi wasallam) described why this happens.
(Bukhari, 3158; Muslim, 2638)
So the brothers and sisters that you love and cherish in this world are with you for a reason.
Al-Khattabi states that people are attracted to those who are like them and people’s souls recognise one another according to their nature.
Finally this sums things up. Ibn Hibbaan narrated: "Ibn Abbas saw a man and said, ‘Indeed he loves me.’ His companions asked, ‘And how do you know?’
(Rawdah Al-Uqalaa, 1/108).