You know what, my husband and I have a similar problem. Don't get me wrong, I LOVE giving blowjobs. It's just that I enjoy sex more, and sometimes he's a one shot guy. So if I do give him a blowjob, I feel like that's it for awhile and it leaves me horny as hell for the next couple of days. So sometimes, I'm reluctant to give him one, then he will start to want one again, and I just hate to get into a cycle like that.
I do have to say that sometimes I exaggerate this situation in my head, but he's willing to except my weaknesses and pound my brains out for a good blowjob.