Can't get off during oral...

So me and my husband LOVE doing 69. After the first time he gave me an orgasm with his mouth, I was hooked. Sadly though in the past 3 years we've been together, he's only been able to do it 3 times. He is so inconsistent and its frustrating because he'll get close and then it's gone. If you have any suggestions please tell me what's worked for you. I don't want to give up 69. I love it too much.