Typically this is determined by how you had the original divorce set up, such as whether he is paying a part of his retirement as a property division or as support, whether it was contractual or merged into a decree, etc.
If the military retirement was divided as part of the marital assets, you cohabiting should not impact your right to receive your share of the property (your share of his retirement account). It would have been unusual to connect your remarriage or cohabitation to your right to continue to receive a share of marital property. If somehow the funds you are receiving are connected to or identified as spousal maintenance, it could be another story. Please get yourself a consult with an experienced family law attorney.
If you receive your miitary retirement pay directly from DFAS on a Military Pension Division Order, under the Former Spouse Protection Act, the payments will end only on the first to occur of the death of the former service member or you. (Payment directly from DFAS depends on having been married to the service member for 10 years during at least 10 years of creditable service.) (Whether there are survivor benefits after his death payable to you depends on whether they were provided for either at the time of your divorce or subsequently. Generally, Survivor Benefit Pay will cease upon your remarriage, and a common law marriage based on cohabitation and "holding out" yourself as married will terminate survivor benefits.)
If you receive your share of the military retirement pay from your former husband, rather than from DFAS, it will be important to look at the court orders to determine whether the portion of military retirement pay that you receive is part of the property division or in the nature of maintenance/alimony. If you are unable to establish that you receive your portion of the military retirement pay as part of the property settlement, it may be modifiable. Your lawyer should be able to help with this.
This answer is given in an open forum and is specifically NOT intended to create an attorney-client relationship. An attorney-client relationship can only be created by a direct or telephonic meeting with this attorney.
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.