@yumian I mean, he does not seem to be that great a person right now but with regards to how he is treating his wife, is she not the one who is 'sending' him multiple other ladies deliberately so he can impregnate them and 'wash his blood clean'? And I think it is ok for them to be surprised by Berta's pregnancy as well, it seems all his other attempts with his wife or the women she pushed at him either failed or resulted in miscarriage so assuming that no children would result from their 3 nights of 'politically obligated sex' is not a huge suspension of disbelief.
The first wife seems obsessed with 'purifying' the King's blood and that seems to upset him. I think he would have been perfectly happy staying loyal and married to only her his whole life. The situation with Berta seems more political and externally motivated anyway.
Not that I am defending his actions either, he seems a bit of an asshole, I wont blame him for being the child of an affair, that is not his fault. It is also likely he only became King because the previous one had no healthy or living children (likely also linked to the intermarriage of relatives resulting in unhealthy babies or reduced fertility that I mentioned in an earlier comment). Making him the only healthy survivor.
Its a shitty situation born of the countries own cultural obsession with 'pure' blood, Berta seems the most logical right now and its OK to pity the main wife but to me it seems much of her misery is her own obsession with having 'pure' children due to her own mindset.