SP, Did you use to offer bj's as a way to opt out of sex?
If so, they may just have a bad connotation now. It may remind him of when you used to offer this instead of sex and he may start thinking, Does she not want sex now? Is this a mercy offering?
Maybe his mind starts running and ruins the experience for him.
At any rate, it's his problem.
Try not to worry about it. Continue to be the nice person that you sure sound like, and he'll come around once the dust settles.
HP
P.S. GGB, I was talking about him performing oral on me. I got off on a tangent and forgot to mention where my mind was wandering. I think he still likes bj's though he only asks or "lets" me do it about once a year.