I've got mixed feelings about Belinda's sudden departure. On the one hand, I'm gutted - she's is a vibrant and colourful character that has made me laugh out loud having been given some extremely funny dialogue in her short time with the show. She also brought a great dynamic to the new Fowler household, establishing them as a family who will have the occasional disagreement or problem to resolve but with a foundation of warmth and humour. The scene with Martin and Belinda was a good example of this - you could see his comedic eye roll at the prospect of having to comfort his wife's extrovert, brash and overly dramatic cousin, but once he realised how genuinely upset she was he was there for her.
On the other hand, if as I suspect, the intention is to have Stacey and Martin leading a family group that is more akin to the original Fowlers - a much vaunted return to the show's core values - then a period where it is just them and their 3 kids trying to navigate their way through everyday life then I can understand why Belinda (and eventually Kyle) need to be gone or at least out of the way for a while.
Nevertheless, I hope she does return in the future.