This is kind of subjective. Every guy is different and what one loves another may not. Ask your man what he likes. He shouldn't assume you just know. I mean, there are basics that most guys like but he could tell you what HE likes and make this a whole lot easier on you. And make ALL guys treat you like a queen. You are not there to service them. good luck
Try switching your technique. Unless he has history of taking forever to get off that way, then that would be an issue for him.
Don't take it personally. It probably isn't you. A lot of couples that have been together for over five years have phases where sex is different, gets boring, one person's preference slightly changes. That doesn't mean they have fallen a out of love it just means you have to communicate, experiment, get creative or sometimes learn from a mistake. The only way to know if it is you is to have another woman come over and give him oral with you there. Althouvb some of us wouldn't mind a that some of us wouldn't even consider it! My guess is that a better solution is that you try something else. You could try 5 minute intervals, you use your hand on him for five minutes then your mouth for five minutes or he can use his hand for five then your mouth for five. You could try having him watch a pornographic video you both agree on while you give him oral. Try a different position like you sitting down and him standing up and after the first five to ten minutes sit still and have him thrust his hips rather than him keeping still while you move your neck and head. Also good for you with your exes for only five minutes wow, I must not do it right either because the only times my past partner's had finished in five minutes was if it were their first oral experience or they woke up with a boner. It could also be that he has some emotional issues with it as well. Some people like oral some people just don't. I totally understand your frustrations on not being able to please your husband. I have had that feeling too. Once I tried all kinds of stuff for three hours and he still couldn't finish. A month later I gave him oral and he finished in less than 15 minutes! Sometimes there are just bad days or even weeks. Don't stop trying but yeah after about 25-30 minutes I would say stop for the night and try again later, don't make yourself too sore! Good for you though for trying that long! Your husband is like mine, very lucky to have wonderfull wife!