OP, if you attack 2nd but reach first, and aimed at a point that will disable the enemy, you won't get hurt, suicide or not.
e.g. if someone tried to suicide at you, but you chopped off their arm
but as everyone has mentioned, it's highly unlikely you'll reach first unless when you execute the move second unless you have a longer sword, or the other guy was not coming straight at you (but the suicider mostly likely would be).