Who is at fault in this situation?

For context, this was on the side of both lanes (think of it like a zipper)

I was on Houston's highway, getting to merge with the other ram. After the dividing line ends, there is enough room for 2 cars for about 200ft.
I was going 50mph, and the other guy was going around 40. My front bumper was at his front window at the moment the line (not lane) ends. With those speeds, my front bumper eventually passed his after around 100ft (around 1.5s later).
Another 1 second passed, I had to brake due the the truck in front of me braking. Decelerating down to 42-ish in 1.5 sec. The guy hit my quarter panel, under my gas window.
By this time, I had already established the lead.