Next year you’ll have to say goodbye to all those American Express rewards points you’ve been racking up with every Costco run:  The two companies have decided to end their longtime partnership. As of March 31st, 2016, American Express cards will no longer be accepted at Costco stores. And those co-branded Costco/Amex TrueEarnings cards with no fees and fabulous rebates? They’re going away too. Costco is said to be working on a new partnership with a different credit card company.