I've come to guess the story unraveling once again! Tessa is pregnant, but not with Pete's. She just told him because she still liked him and needed support. The baby is actually William's, but Lexi think's it's Pete's. In the end they all figure it out and Lexi finally does have Pete's baby and they lived happily ever after, even though one baby's real father is Will. Billiam. Becks the secks.
Only, that's just a guess.
I love this story.