UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)

Affinity Gaming

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

Not Applicable

(CUSIP Number)

James A. Cacioppo

Managing Partner

One East Capital Advisors, L.P.

225 NE Mizner Boulevard, Suite 720

Boca Raton, FL 33432

(561) 210-4640

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

September 8, 2015

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Sections 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ¨

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Section 240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934, as amended (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. Not applicable

CUSIP No. Not applicable

CUSIP No. Not applicable

CUSIP No. Not Applicable

Item 1. Security and Issuer

This Amendment No. 4 (“Amendment No. 4”) amends and supplements the statement on Schedule 13D originally filed by the Reporting Persons on June 7, 2013 and amended on October 15, 2013, December 5, 2013 and June 4, 2015 (as amended as of the date hereof, the “Schedule 13D”) relating to the common stock, $0.001 par value (the “Common Stock”) of Affinity Gaming, a Nevada corporation (the “Issuer”). The address of the executive offices of the Issuer is 3755 Breakthrough Way, Suite 300, Las Vegas, Nevada, 89135.

Unless otherwise indicated, each capitalized term use but not defined in this Amendment No. 4 shall have the meaning assigned to such term in the Schedule 13D.

Item 4. Purpose of Transaction

Item 4 is hereby supplemented as follows:

On September 8, 2015, the parties to the Agreement executed Amendment No. 4 to the Agreement, a copy of which is attached as Exhibit 99.6 to this Amendment No. 4 and incorporated by reference herein, in order to add Barclays Bank PLC (“Barclays”) as a party to the Agreement. Other than the addition of Barclays as a party, all terms and conditions of the Agreement as previously disclosed on this Schedule 13D remain in full force and effect without amendment.

Item 6. Contracts, Agreements, Understandings or Relationships with Respect to Securities of the Issuer

Item 6 is hereby supplemented as follows:

See description set forth in Item 4 of this Amendment No. 4, which is incorporated herein by reference.

Item 7. Material to be filed as Exhibits

S I G N A T U R E

After reasonable inquiry and to the best of our knowledge and belief, the undersigned certify that the information set forth in this statement is true, complete, and correct.

Date: September 9, 2015

EXHIBIT 99.5

JOINT FILING AGREEMENT

The undersigned acknowledge and agree that the foregoing statement on Schedule 13D is filed on behalf of each of the undersigned and that all subsequent amendments to this statement on Schedule 13D shall be filed on behalf of each of the undersigned without the necessity of filing additional joint filing agreements. The undersigned acknowledge that each shall be responsible for the timely filing of such amendments, and for the completeness and accuracy of the information concerning it contained therein, but shall not be responsible for the completeness and accuracy of the information concerning the others, except to the extent that such person or entity knows or has reason to believe that such information is inaccurate. This agreement may be executed in any number of counterparts and all of such counterparts taken together shall constitute one and the same instrument.

Date: September 9, 2015

Exhibit 99.6

AMENDMENT NO. 3

This AMENDMENT NO. 4 (this “Amendment”) is made and entered into as of September 8, 2015, with reference to that certain Agreement, dated as of May 29, 2013 (as amended, supplemented or otherwise modified in accordance with the terms thereof, the “Stockholders Agreement”), by and between each of the parties thereto (each such entity and any other person who becomes bound by the Stockholders Agreement as contemplated by clause (a) of Section 1 thereof, a “Stockholder” and collectively, the “Stockholders”) and Barclays Bank PLC (the “Joining Party”). Capitalized terms used herein and not otherwise defined shall have the meanings ascribed to such terms in the Stockholders Agreement.

WHEREAS, as of the date hereof, the Joining Party owns the Shares set forth under its signature hereto;

WHEREAS, the Joining Party desires to be made a party to the Stockholders Agreement and the other Stockholders party thereto desire to accept such joinder;

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt and sufficiency of which is acknowledged, and intending to be legally bound, the Stockholders and the Joining Party agree as follows:

1. Joinder. The Joining Party shall be deemed to be a party to the Stockholders Agreement as of the date hereof, shall be deemed to be a “Stockholder” for all purposes thereunder and shall have all of the rights and obligations of a Stockholder thereunder as if it had executed the Stockholders Agreement.

2. Representations, Warranties and Undertakings of the Joining Party: The Joining Party: (a) hereby agrees to be bound by and comply with all of the terms, provisions and conditions contained in the Stockholders Agreement, (b) represents and warrants to each other Stockholder, as of the execution of this Amendment, that it can, and hereby does, make the representations and warranties of the Stockholders set forth in Section 3 of the Stockholders Agreement (provided that all references to the “Currently Owned Shares” set forth in such Section 3 shall be deemed to refer to the Shares set forth below the Joining Party’s name on the signature page to this Amendment); and (c) acknowledges and agrees that the undertakings set forth in this Amendment are for the benefit of, and may be enforced by, each Stockholder.

3. Restrictions on Transfer. Section 1(d) of the Stockholders Agreement shall be amended and restated in its entirety as follows: “(d) such Transfer is by either (i) Highland Capital Management LP, (ii) Spectrum Group Management, LLC, (iii) One East Partners Opportunities, L.P. and One East Partners Master, L.P., acting together, or (iv) Barclays Bank PLC (each, in such transferring capacity, “Transferring Owner”), representing a Transfer of all or a portion of the Owned Shares held by such Transferring Owner, to SPH Manager, LLC, after not less than five (5) business days’ notice of the proposed Transfer to each other Stockholder.”

4. Miscellaneous. Except for clauses (a), (d) and (l) thereof, Section 5 of the Stockholders Agreement is incorporated herein, mutatis mutandis.

5. Effectiveness. This Amendment shall be effective as of the date first written above by and among each Stockholder that has executed this Amendment as of such date.

6. Ratification. Except as specifically modified herein, all terms and conditions of the Stockholders Agreement are hereby ratified and confirmed in all respects and shall remain in full force and effect.

[Signature page follows.]

IN WITNESS WHEREOF, each of the parties has caused this Amendment to be duly executed as of the day and year written above.