Complex sentence: Tamsin is also pregnant, as the result of a one-night stand with a guy from university, and she and Virginia decide to raise the child together-until Tamsin realises that Virginia is still obsessed with Megan.
Split into simpler sentences: Tamsin is also pregnant, as a result of a one-night stand with a guy from university. Tamsin and Virginia decide to raise the child together, until Tamsin realises that Virginia is still obsessed with Megan.