I get your point but losing his memories still shouldn't be a justification for being a huge dick. Moreover, he never really gave Jian any proper time as well to explain when needed and kept jumping into conclusions without trying to confirm whether those accusations were accurate.
the Seme keeps avoiding trying to take accountability and gets surprised when his bad behavior actually results into not getting what he wants. That reflects his character, regardless of his memory loss.

i cant be the only on that feels bad for the seme. Like he lost his memories just before proposing. Then after he regains it back, his mate says that the baby is not his and is instead his bothers. Like ik he was shitty, but it was also during the time where he needs to get his mind all sorted out. He still thinks he was that guy a few years back so he was probably shocked at why they were dating