Ruby, 80 76 bytes

-4 bytes thanks to manatwork

puts"\\";$*[i=0].chars.each_cons 2{|b,c|puts" "*(b==c ?b==?/?i-=1:i+=1:i)+c}

Gets the input as a command line argument

Explanation:

puts "\\"           # Output the first backslash
$*[i=0].            # Get the first argument and set i to 0
chars.              # Go through every individual character,
each_cons 2 { |b,c| # In pairs to compare easily
                    #
    puts " " *      # Decide how many padding spaces to use based on the value
                    # of i. The expression inside the parenthesis will return
                    # i but before that, it will increment/decrement i based
                    # on what the previous character was.
                        #
    ( b==c ?            # if b == c
        b==?/ ?         #   if b == "/" (Going to the left)
            i-=1        #       return decremented i
            :           #   else        (Going to the right)
            i+=1        #       return incremented i
        :               # else
        i) +            #   return i
                    #
                c   # Finally, write the second of the characters that we're
}                   # iterating through.

Ruby, 80 76 bytes

-4 bytes thanks to manatwork

puts"\\";$*[i=0].chars.each_cons 2{|b,c|puts" "*(b==c ?b==?/?i-=1:i+=1:i)+c}

Try it online!

Explanation:

puts "\\"           # Output the first backslash
$*[i=0].            # Get the first argument and set i to 0
chars.              # Go through every individual character,
each_cons 2 { |b,c| # In pairs to compare easily
                    #
    puts " " *      # Decide how many padding spaces to use based on the value
                    # of i. The expression inside the parenthesis will return
                    # i but before that, it will increment/decrement i based
                    # on what the previous character was.
                        #
    ( b==c ?            # if b == c
        b==?/ ?         #   if b == "/" (Going to the left)
            i-=1        #       return decremented i
            :           #   else        (Going to the right)
            i+=1        #       return incremented i
        :               # else
        i) +            #   return i
                    #
                c   # Finally, write the second of the characters that we're
}                   # iterating through.

Ruby, 80 bytes

puts"\\";$*[i=0].each_char.each_cons 2{|b,c|puts" "*(b==c ?b==?/?i-=1:i+=1:i)+c}

Gets the input as a command line argument

Explanation:

puts "\\"           # Output the first backslash
$*[i=0].            # Get the first argument and set i to 0
each_char.          # Go through every individual character,
each_cons 2 { |b,c| # In pairs to compare easily
                    #
    puts " " *      # Decide how many padding spaces to use based on the value
                    # of i. The expression inside the parenthesis will return
                    # i but before that, it will increment/decrement i based
                    # on what the previous character was.
                        #
    ( b==c ?            # if b == c
        b==?/ ?         #   if b == "/" (Going to the left)
            i-=1        #       return decremented i
            :           #   else        (Going to the right)
            i+=1        #       return incremented i
        :               # else
        i) +            #   return i
                    #
                c   # Finally, write the second of the characters that we're
}                   # iterating through.

Ruby, 80 76 bytes

-4 bytes thanks to manatwork

puts"\\";$*[i=0].chars.each_cons 2{|b,c|puts" "*(b==c ?b==?/?i-=1:i+=1:i)+c}

Gets the input as a command line argument

Explanation:

puts "\\"           # Output the first backslash
$*[i=0].            # Get the first argument and set i to 0
chars.              # Go through every individual character,
each_cons 2 { |b,c| # In pairs to compare easily
                    #
    puts " " *      # Decide how many padding spaces to use based on the value
                    # of i. The expression inside the parenthesis will return
                    # i but before that, it will increment/decrement i based
                    # on what the previous character was.
                        #
    ( b==c ?            # if b == c
        b==?/ ?         #   if b == "/" (Going to the left)
            i-=1        #       return decremented i
            :           #   else        (Going to the right)
            i+=1        #       return incremented i
        :               # else
        i) +            #   return i
                    #
                c   # Finally, write the second of the characters that we're
}                   # iterating through.

Ruby, 80 bytes

puts"\\";$*[i=0].each_char.each_cons 2{|b,c|puts" "*(b==c ?b==?/?i-=1:i+=1:i)+c}

Gets the input as a command line argument

Explanation:

puts "\\"           # Output the first backslash
$*[i=0].             # Get the first argument and set i to 0
each_char.          # Go through every individual character,
each_cons 2 { |b,c| # In pairs to compare easily
                    #
    puts " " *      # Decide how many padding spaces to use based on the value
                    # of i. The expression inside the parenthesis will return
                    # i but before that, it will increment/decrement i based
                    # on what the previous character was.
                        #
    ( b==c ?            # if b == c
        b==?/ ?         #   if b == "/" (Going to the left)
            i-=1        #       return decremented i
            :           #   else        (Going to the right)
            i+=1        #       return incremented i
        :               # else
        i) +            #   return i
                    #
                c   # Finally, write the second of the characters that we're
}                   # iterating through.

Ruby, 80 bytes

puts"\\";$*[i=0].each_char.each_cons 2{|b,c|puts" "*(b==c ?b==?/?i-=1:i+=1:i)+c}

Gets the input as a command line argument

Explanation:

puts "\\"           # Output the first backslash
$*[i=0].            # Get the first argument and set i to 0
each_char.          # Go through every individual character,
each_cons 2 { |b,c| # In pairs to compare easily
                    #
    puts " " *      # Decide how many padding spaces to use based on the value
                    # of i. The expression inside the parenthesis will return
                    # i but before that, it will increment/decrement i based
                    # on what the previous character was.
                        #
    ( b==c ?            # if b == c
        b==?/ ?         #   if b == "/" (Going to the left)
            i-=1        #       return decremented i
            :           #   else        (Going to the right)
            i+=1        #       return incremented i
        :               # else
        i) +            #   return i
                    #
                c   # Finally, write the second of the characters that we're
}                   # iterating through.