Garon didn’t know until the MC told him just then about the bond. The MC stays with Garon at first to kill him, and then later because he’s in love with him. Raon is fine, he ends up in a small town as a sort of head figure. As to if Raon can feels the MC’s love for Garon, it’s unknown. The MC separates from Raon right after Raon names him.
Okay, so my memory is a little weak since it’s been a year since I read the novel!! But basically, Raon launches a surprise attack on the empire with a small army. Raon and Garon end up fighting with the intent to kill each other. Garon starts dying. The MC is right there in tears and tries to give Garon the antidote (which is dangerous for the MC), but Garon keeps stopping him, not wanting the MC to suffer. When Garon finally passes out from loss of blood and can no longer fight back the MC gives him the antidote. BUT!! Raon takes the MC away before he can see if the antidote works. Raon and the MC go far away to a village at the end of the continent full of refugees. The MC moves in with Raon and teaches art to the village children, but ever since he watched Garon die he’s been crying and sleepwalking through the town, trying to leave in his sleep. One night the MC wakes in the middle of him sleepwalking and Raon throws him to the floor and asks him why he’s trying so hard to leave, then if the MC knows Garon is actually alive. The MC can’t answer, be he heard gossip from the villagers and did know. More time passes. The MC doesn’t get better. Eventually, Raon asks MC if he should let him go. The MC can’t say anything at first, but after choking up he starts sobbing and says, “Please let me go.” So, yeah. Raon knew the MC couldn’t move on from what happened.

From what I've read in some comments (spoiler ahead)
The brother named the MC but MC still ended up with the seme...
Did the seme know about the soul bond?
Why did MC stay with the seme and not with the brother? Was he still being threatened or did he fell in love?
What happened to the brother at the end?
If MC eventually fell in love with the seme does that mean the brother can feel his love to the seme because of the bond? That would be torture...