Heart vs. brain

I always gave the best advice to my friend from a single guy points of view. A pristine perspective from someone who has never encountered love or something similar. I always asked them "what does your heart   tells you what to do?" then i asked again "what does your brain tells you?". They listened and I always listen to what they told me about their experiences so i hoped that i could never encounter similar situations or solve it quickly. I am dead wrong. Now, I'm stuck in the same situation and simply clueless. My brain tells me to hold, but my heart tells me to act. If i hold, I'm afraid if he thinks that i disappear therefore cut all contacts with me or just to get myself ready to act later with a cold head and most likely cold heart. If i act now, there's four possibilities first he won't reply, therefore it ends there, second he replies but he won't lived up to my expectation and i might ended up more disappointed, third he replies and realized that i have feelings for him and that turns him off or the forth scenario is the happy ending, the start of something good. I know i shouldn't expect much from him or all this experience but I just can't help it. When you are stuck in this situation, you feel the ecstasy and agony at the same time and you can't think clearly. A friend told me don't expect anything and I have to try to let him go. I guess that is the best advice.