Boyfriend began stuttering again - gotten worse over past year or so. Any advice?

Boyfriend began stuttering again - gotten worse over past year or so. Any advice? We met in High School and honestly, if he never told me he had a stutter, there would be no way I could guess it. Sure, there were some words I caught onto after he told me, but I figured that wasn't even bad. Everyone stutters once in awhile... Anyways. Here are some things to note: 1) Stuttering runs in his family. 2) He went to STARS for speech therapy during most of his childhood. 3) Part of his therapy was recording his voice and playing it back. Other than that, there's not much I know about the condition. Fast forward about five years and I began noticing the stutter developing more and more. He gets really frustrated, which is the bad part but I'm incredibly patient and even though I often finish his sentences, I never do it when he's in the middle of a stutter. Are there any tips or advice? Anything I can do to help? I hate seeing him get so frustrated, and that it is clearly getting worse after all this time concerns me.