5.) when she has the ring in hand and says that she can't wear this or else others will notice..he tells her "it's okay...you're with me"....to me, this whole entire line was enough for tang wei to decide what to do..she was neglected by her father, lonely and weary....her aunt didn't care for her..the resistance leader didn't give a damn about her wellbeing..wang leehom disappointed greatly when she needed him most

....so when tony says this....she really was touched and felt that she belonged somewhere..her decision wasn't completely irrational, she may be
confused..but I can see WHY she has chosen this path.