Welcome to the forum!! There are lots of honest people here who are willing to share!! Polyamory is based on honesty. I always disclose I am polyamous from the very beginning. To me, it doesn't seem to be very thoughtful to wait until someone is getting attached or falling in love before telling them. Just wondering how long you have known him. It might help us to understand if we have a better idea of how long the "falling in love" process took for you!
And welcome again!!
The key to life is in being fully engaged and peacefully detached simultaneously and authentically in each moment.