How to use “know” and “realize” correctly

Question

Are they just actually the same? Especially as in the following examples:

I realize then whom I love.
I know then whom I love.

Answer 1

To know something describes a steady state. To realize something is to transition from a condition of ignorance into knowledge. If you put it into a timeline, when you realize something you change from not knowing to knowing:

<--- I don't know X ---| I realize X |--- I know X --->

To realize contains the additional connotation that your knowledge is gained by introspection, contemplation, or a change in self-awareness. If someone merely tells you something, you wouldn't say I realized X. You would say instead I learned X or something similar. When you realize something, you assert that you've come to that knowledge under your own power.

Answer 2

If you realize that you're in love, then you have just had a revelation about where your feelings lie. One of the definitions of realize is:

to grasp or understand clearly.

To know something is more long-term, perhaps after having realized it. The first definition for know is:

to perceive or understand as fact or truth; to apprehend clearly and with certainty

They sound similar, but in usage to realize something is more of an "aha!" moment, while knowing something can last far longer than that. It may take you a while to come to a realization, but you will not actively realize something for a long period of time.