Girl, I feel you! That’s one of the most frustrating sexual things: lack of reciprocal giving. He probably enjoys you going down on him so much that I am tempted to advise you to go nil-by-mouth below the waist just to see his reaction. However, that is not a solution. You have asked several times and he hasn’t given you a reason as to why he can’t or won’t. If he has hang-ups related to hygiene, tastes etc, he should have communicated the same and both of you would have looked for a solution.
Having said that, this could be an indication of the state of your relationship as there are different perspectives based on the kind of relationship you are in. Unfortunately, you didn’t indicate if you are married, in a long-term relationship or a friend-with-benefits situation. In a relationship, most guys would love to have as much sex as possible before deciding if you are the ‘one’ or not. Unfortunately, sex or sexual prowess is rarely the qualifier of marriage. If he is not serious about the relationship, it might be one of the reasons he may not want to commit and go down on you.
If you are in a serious relationship or marriage, there are gaps in your relationship, especially in the communication department. He could be one of those old fashioned, traditional men who believe sexual bliss is exclusively for the man’s pleasure; the same attitudes that lead society to circumcise women. Some are simply just selfish. Nevertheless, if this man loves you, he will move mountains to make you happy. You, therefore, must talk to him and find out why he would not go down on you and this time, make it clear you have already given him enough time.
So as I mentioned above, if it is just an issue of hang-ups like hygiene concerns then you can take a bath together as a way of building confidence and intimacy. As for taste, you can incorporate tasty treats such as flavored lubricants, honey, whipped cream and even lust dust or maybe ice cream if you can take the cold.