I beg to differ, because that's not what I got from watching the episodes.
First, he joined Nurhachi's army on the suggestion of his gf's grandpa (you know, who is an elder of the Wudang sect) to infiltrate them. For that purpose, he also has to gain Nurhachi's trust. He, along with his gf & gf's grandpa, very well understands that Nurhachi wants to use him.
Second, he trusts Dongfang Liang, because during his journey to Shaolin Dongfang Liang has been very supportive and always tried to help him. I think it's pretty. clear from the whole episodes that despite his ambition to be a great swordsman, Dongfang Liang is actually an upright and decent person. He was deceived by Mou Yiyou, thinking that Yujing betrayed him. And speaking of Mou Yiyou, if you've reached episode 29, you must have seen that he's switched sides to the Kunlun clan, aka the same clan with Dongfang Liang, and the clan that is on the same side with Wudang. Kunlun clan has been helping Yujing and his adopted sister.
https://www.youtube.com/watch?v=WddbkB5Oq70&list=PLJPEbKQEnORNJMWEN2EscXe80kra2OZW9
Second, he trusts Dongfang Liang, because during his journey to Shaolin Dongfang Liang has been very supportive and always tried to help him. I think it's pretty. clear from the whole episodes that despite his ambition to be a great swordsman, Dongfang Liang is actually an upright and decent person. He was deceived by Mou Yiyou, thinking that Yujing betrayed him. And speaking of Mou Yiyou, if you've reached episode 29, you must have seen that he's switched sides to the Kunlun clan, aka the same clan with Dongfang Liang, and the clan that is on the same side with Wudang. Kunlun clan has been helping Yujing and his adopted sister.