I'm a Malaysian and have been in the UK for 5 months under my visa-free leave to enter for 6 months. I took a break from my career and packed my bags to be with my partner, who is a British citizen, and travelled around Europe together. I'm going back next month February 25th as my passport was stamped on August 28th (marks almost 6 months in the UK) and I'm planning to come back here for summer holiday with my partner and travel around Europe again. I'm now wondering if there is a cooling period, before I am allowed to enter the UK again.
There isn't a formal cooling off period.
However there is a rule that you should not attempt to live in the UK through frequent or sucessive visits. If you start spending too much time in the UK then they are likely to get you on this but exactly how much is too much is at the descretion of the border guard.