"I remember the part that she fell on top of him.. Oh my gosh.... It looked like she was trying to take advantage of him... "
She wasn't at first, it was an accident -- he was very weak and she was off balance since she could only use one hand. People fall on top of each other a lot in this series...
"Why did Tong Bo agree to marry Tian Xue if he liked Dou Dou. I know that Yin Zhong made them, but why did they abide to his wishes?? Were they blackmailed???"
In a way, yes. Here's the way I understand it: The valley where the Tong boys lived is trapped in ice. By the time Yin Zhong suggests the marriage, they've seen ample evidence that he has great power. (They don't know his true identity and think of him only as Yin Hao's brother.) They think he can help them unfreeze the valley. So they go along with it.
Yin Zhong wanted Tong Bo to marry Tian Xue because he mistakenly believes Tong Bo to be the leader of the valley people. His information came from Tong Xin, who did not know that their father at the last minute had named Tong Zhan leader instead. I believe Yin Zhong thinks that this marriage will re-establish an alliance between the Houses, and then Tong Bo will be obligated to behave toward YZ as an honoured family member and let him in on all the valley's secrets. YZ wants this because he is out to achieve immortality and wipe out all the Tongs.
"When did Zhao Yun start liking Tong Bo?? Did he know that she liked him?"
Again, I'm pulling this out of my hat because I don't understand most of what they're saying; I think she started liking him when she saw him in the bath, even though she was also embarrassed. Plus the fact that he was kind to her and sympathetic about her hand. I believe she confessed to him that she liked him, but he was already interested in Dou Dou.