▲ Chuck and Blair ≈ Rufus and Lily ▲
Bart asks Lily to marry him and she says yes despite it’s she still has feelings for Rufus. (1.11)
Louis aks Blair to marry him and she says yes despite it’s clear she still has feelings for Chuck. (4.20)
Lily betrays Bart with Rufus before of their wedding, and Bart knows. (1.18)
Blair betrays Louis with Chuck despite she is engaged. I do think Louis suspects it. (4.22)
Lily: Well there is a comfort in revisiting the things that we loved when we were young.
Bart: But the truth is I’m not that young man anymore. I think maybe I’ve outgrown it. And holding onto it is keeping me from moving forward with what’s most important to me now. What do you think I should do?
Lily: I think you should let it go.
Bart: I agree. Now can you do the same for me? (1.18)
Lily marries Bart anyway, Rufus decides to let her go. (1.18)
Blair decides to remain with Louis after Chuck lets her go. (4.22)
Rufus: And here we go. Are you sure about this?
Lily: Ask me again and I’ll change my mind.
Rufus: I love you, Lily.
Lily: I love you too, Rufus. (1.18)
Blair: It’s taking all the power I have to walk away from you.
Chuck: I know. But I need to let you go. You need to let go.
Blair: I’ll always love you.
Chuck: I will always love you. (4.22)
Lily kept hiding to Rufus they had had a baby 20 years before. Bart found out thanks of his PIs, Rufus in 2.13. They reunited and accepted him in their family the day they got married and that Scott finally revealed them who he was. (3.05)
Since both Ed and Leighton confirmed someone is pregnant and didn’t say who, my bet is that Blair is and that she will either hide the pregancy or tell Louis the baby it’s his. Chuck will eventually find out sooner or later, and maybe they can also be a family and get married (+ a baby?)