Yes but you need also to understand his past life! Also he do not know that Liz is his sister.
He drug, he fuck, he was free until he was adopted? From the principal.
So you need also to immedesimate in him. With a life like that, he grow up with a shitty mind.
But here where i say... this are all in the developer hand. Because now with this game, the developer can let us shape his future. Become more mature and sweet or behing an asshole.
Is for that, that i say... i hope that the developer give us the choice.
Anyway yes sometime he is a prick expecially in ch5 as you say. (sorry i am not so good in english so i hope write all well till now XD) but sometime he can be also sweet with ppl who like him. And i think that the developer let Brian mature more during the course of the game. At last i hope.
Anyway the game is start just now. I mean only 6 chapter. I expect more and more mature thing till the end of the game.
I also wanna see how the developer manage the optional incest thing (i think is optional, because not all ppl are like me, that wanna play the incest game). So i really wanna see how he write the incest and the sex thing with Brian and his mother and alf sister. Cant wait to make love with the mother and Lizzie after i unlock the incest secret.
This thing really excite me so much
but... i am like 80% sure that the deep secret about incest, it will be unlockable only after having sex with her a couple of times. Otherwise I strongly doubt that she let Brian do sex with her. Discover that she is Brian mother, really become hard for her to do sex with him.
But if the two already had sex, the thing become different and she can be a little bit open toward sex thing with her son.