Wai-Tung decides to marry Wei-Wei so that she can get her green card and he can pretend to be straight to his parents who are arriving from Taiwan. On their wedding night they get drunk and end up having sex.
When Wei-Wei learns she's pregnant, it strains Wai-Tung's relationship with Simon, but she decides to keep the baby and asks them to both be the father - they accept. Wai-Tung comes out to his mother who, despite hoping he will get over it, is too overjoyed at the prospect of a grandson.
Simon learns that Wai-Tung's father speaks English and has long ago figured out their relationship, but he promises not to tell, as the father likes his secrets.
Thanks Mary C!