I'm the only child now because my brother passed away 2 years ago
Oh no I'm sorry to hear that!  Technically, though,  "only child" is generally applied only to those individuals who have never had siblings.
Oh, I didn't know that. 
No worries! Actually, throughout history, only children were pretty uncommon as many families had multiple children.
I wonder why? Maybe because they didn't have condoms
That's definitely possible! Though, the use of condoms foes back at least several centuries, so no excuses on that!
or maybe people just wanted to have more than 1 kid
Yes, that's the most likely reason - more kids means more help around the house, and more help in the fields, so big families were pretty common.
That makes sense!
Exactly! Myself, I have two siblings - both older brothers, so I'm the baby of the family!