Well he said he can’t get married....I assume it’s because he is gay and gays can’t get married? So yea I would also think it’s the uncle and that why the interest in uke since he looks similar
Especially when the seme is touchy feely with the uke and says that he looks similar to his uncle every year The author gives hint on lingering feelings here and there so... yeah
Seme is definitely in love with the uncle and that's the person he can't move on from