I too am in love and struggle with this same question. I can offer my solution. Use both. Enjoy the endorphine rush of the feeling of love ( which is the heart so to speak.) But realize why you ask the question. There is obviously a reason for your aprehension of completely letting go. Use your brain and decide to what degree you should allow your heart to pilot your emotions then deal with this person as so you conclude. Do not sell yourself short. Could the problem be one that you should resolve within yourself or is there an actual problem?
use ur heart or brain??