Bipartite cuts in Ramsey-Turán style

We prove that every $K_5$-free $n$-vertex graph with sublinear independence number can be made bipartite by removing at most $n^2(1\mathrm{/}18+o(1))$ edges, where the constant $1\mathrm{/}18$ is best possible. The proof method is related to extensions of Turán Theorem in edge-weighted settings, and part of the proof uses flag algebra.