If the love of your life abandoned you, then didn't even recognise you as adults and to rub salt into the wound just used you to prevent you from talking out in the media about them money laundering, wouldn't you want revenge? Taekyung had the power, connections and means to get revenge, but in the end he couldnt shake off his love for Heejae, and tried bring down his company, but protect him from the fallout.
Remember, from his perspective Heejae wasn't the innocent marshmallow that we know him to be - you cant blame him because nobody told him the truth.
He's a likable character since even after he knew that him tormenting Heejae for revenge were all caused by a misunderstanding, he immediately and sincerely apologizes to Heejae. Even though Taekyung was also a victim by the hands of Heegyum, he still bravely acknowledges his "mistake" even though he didn't know anything in the first place. He acknowledges that he hurt Heejae even though that hurting was only planned out of anger that was caused by Heegyum.
In short, even though he was blinded by Heegyum, and even though it wasn't his fault to grow mad against Heejae, he still wholeheartedly and sincerely asked for forgiveness to Heejae. He cried for hurting him which he didn't mean to if only Heegyum didn't cause all those misunderstandings. He stood up for his mistakes even though it was caused indirectly by someone else. He was hurt too, but he still embraced Heejae first. He always put Heejae first.
BRUH someone please convince me to forgive taekyung I can’t see anything good about him so friggin help me out