I've always had ups and downs with my stutter. I'd have months where i thought I has conquered it for the most part, only to have it return in full force because stress or lack of sleep or anxiety or no reason at all. And the more I'd focus on it the worse I would get It's frustrating and sometimes embarrassing and humiliating to have to go through these ups and downs especially when you've put effort and money into achieving fluency and especially around people who have only known you while you've been in control of your stutter Honestly I would stop asking him how you can help. You really can't do anything to fix it and doing so is serving as a constant reminder to him of how bad his speech is. There's no magic technique that we can tell you to teach him. Just create a comfortable environment for him, act normal around him, give him all the time he needs to get his words out, don't looks distracted or look away when he's having a hard time getting words out, etc.