You are misunderstanding what that ruling means.

Gonzales filed suit in the United States District Court for the District of Colorado against Castle Rock, Colorado, its police department, and the three individual police officers with whom she had spoken under 42 U.S.C. §1983, claiming a federally protected property interest in enforcement of the restraining order and alleging "an official policy or custom of failing to respond properly to complaints of restraining order violations."

And the ruling,

The Court's majority opinion by Justice Antonin Scalia held that enforcement of the restraining order was not mandatory under Colorado law; were a mandate for enforcement to exist, it would not create an individual right to enforcement that could be considered a protected entitlement under the precedent of Board of Regents of State Colleges v. Roth; and even if there were a protected individual entitlement to enforcement of a restraining order, such entitlement would have no monetary value and hence would not count as property for the Due Process Clause.

So it has no bearing on whether or not police are obligated to protect citizens. Setting aside the bit which is just about Colorado state law they just said that a citizen's right for a particular law to be enforced does not create grounds for a monetary claim of damages should the officers fail to enforce the law.