There are a number of problems with that design.
The diagram will be clearer and easier to follow if you put the 0V rail along the bottom and the positive rail across the top. Also, having the relay shown separately adds a lot of unnecessary confusion and opportunity for error.
I would use a grunty N-channel MOSFET instead of a relay. A good choice would be the NTD4906; see
http://www.digikey.com/product-detail/en/NTD4906N-35G/NTD4906N-35GOS-ND/2194521
I would sense the light bulb current in the source lead of the MOSFET. This allows you to use a standard single-supply op-amp or comparator to detect the bulb current.
Bulb current will be a lot higher than nominal, and will not accurately reflect the bulbs present, at the start of each flash. You need to sample the bulb current shortly before the end of the flash.
You also need to latch the result of the current comparison somehow, so the oscillator speed will be steadily either slow or fast. The way you've designed it at present, the comparator output will go high and low with the flashing, and this won't give you a steady fast/slow signal to the oscillator.
Your comparator needs to have a reference voltage to compare the shunt resistor drop to. I would use a voltage divider across the supply voltage, because the supply voltage will also affect the bulb current.
You've probably already discovered that connecting the transistor to the 555 in that way doesn't work. There is no simple way to do it, that I know of. My best guess at a possible solution would involve three transistors.
You still haven't given any background information on your project, and you have ignored most of the questions I have asked so far, so I can't make any more specific suggestions.