i've seen a lot of people talking about barth being tanrak's gay awakening, and while i do believe that to be partially true, i personally believe tanrak was already aware of his homosexual desire before barth came along. it's just that barth is the first real physical 'temptation' that tanrak's had to deal with.
the thing that really gave it away for me was the last scene in episode 1, but honestly i think tanrak was tipping his hand that whole episode. he's presented as this model student, the father's golden child, practically a priest in training. and yet despite the fact that the father asked him to perform his duties as the good catholic and look after barth - the foreigner in their land as mentioned in the beginning of the episode - tanrak doesn't really do that. in fact the absolute bare minimum, holds barth at arm's length as much as possible, pretends not to see. and that doesn't jive with the impression we're supposed to have of tanrak, which is kind and jovial and easy going and above all else, obedient. and yet he's almost cold with barth, all but abandons him to fend for himself. yes, we the audience see the conflict in him over it (bc tanrak is, ultimately, kind) and yes he comes around in the end but the reality is that he still acted out of character, still wanders into the murky grey zone of not disobeying the father but not exacrly doing as he tells him either. still turned his back on barth when he was all alone, even if he did hesitate. even if barth didn't see him turn away.
a character like tanrak is not going to behave like that for no reason (especially not when contrasted with how we see him behaving in ep 2, and even at the end of ep 1). he clearly values his faith above all else at this point in the narrative - and yet the way he treats barth initially does not honour that faith. why? well, because tanrak knows temptation when he sees it. (what is it he said about the painting? 'along the path beasts devour sinful humans and tempt people off the path?')
but maybe even more importantly than even that is the fact that tanrak can see barth being othered. and he knows the good, christian thing to do would be to step in, protect the foreigner in his land, defend the weak and the fatherless, uphold the cause of the poor and the oppressed - that's what's expected and asked of him (hence why the father is so harsh with him in ep 2 - not just because he handled the situation 'badly', but bc he shouldn't have allowed it to even get to that point in the first place). he's supposed to stand with barth, and yet he turns away. because tanrak is smart, and more importantly he's self aware. he knows what he is. he knows his hands are not clean. and he knows the last thing he needs is to bring undue attention to himself, or to stand out to his peers in any way - especially not to defend the new violent queer kid.
if the attention is on him and people look too closely or ask too many questions, then they're more likely to notice the thing tanrak is trying so desperately to hide.
the last scene of episode 1 is what really gave him a way. episode 2 confirmed that tanrak isn't particularly afraid about getting into trouble, or adverse to breaking some rules. and yet he had such a big reaction when they were caught in that last scene - you could literally feel the panic building and the walls closing in on tanrak. dread was written all over his face. but he didn't have that reaction bc he was caught and might get in trouble. it was because he was caught with barth. alone together and had been all night. he knows how that looks. he knows what people might think, what they might say. because tanrak, who on some level is already aware that he's gay, is hyperaware of that perception of him. and now, after trying so hard for so long to be good, he thinks he's been caught out.
of course, he hasn't been. not yet. but the guilt of allowing them both to end up in that position in the first place all but ties him to barth after that (and it's unwarranted guilt yes, but understandable too. he didn't do what was asked of him by the father. he didn't behave as a good catholic in the way he treated barth. and because he was trying so hard to protect himself, he dishonoured god and barth ended up hurt. of course he's gonna prey for redemption for that). he has been entrusted with barth's care. he will look after him. and he will not be pulled off the path in the process, but rather pull barth to him. but in order to do that, he has to let barth in, at least a little bit. and that's an awfully slippery slope. now he's lying for barth. now he's opening up to him. now he's playing along, getting in more trouble, allowing himself to be touched. to touch. shoulders, fingertips. thighs. in the dark, behind people's backs.
we all know how it ends. i think tanrak knew how it was going to end, too, deep down. it's why he allowed himself to act out of character in order to keep barth at arm's length. it's why he prays the rosary, asks for redemption in advance. when asked what for, he looks up at barth and it's an answer. lust means letting desire control us. what if you can't stop it? then you fight it. but the tree of the knowledge of good and evil is extending a branch, offers temptation, says come on, just a bite. tanrak couldn't even bring himself to touch barth in that scene, did you notice? he pushed his arm away with the end of his pen. fighting it.
but the tree says, i'll help you up. says, next time i can come here with you. says, why fight it?