Your book is incorrect.
The Catholic Church does not prohibit bringing sexual pleasure to your spouse, or using your mouth to do so.
What it does prohibit -- and rightly so -- is using another person as a sexual object of personal gratification, and it prohibits perverting the marital act of sex between spouses. What this means, in graphic practicality, is that one should not purposefully stimulate the male to the point of ejaculation outside of marriage, or outside of the natural sexual act.
Don't mean to offend you, but you are (obviously) a child. There is no way you are going to be able to understand all of the Church's teachings or the philosophy behind them. Most people don't even try (you can see from the many other absurd posts on this issue). It is one thing to say "I don't understand this," and another to determine that your understanding is what makes something correct or erroneous.
I have yet to find ANY person who actually understood the Church's teachings and disagreed with them -- maybe couldn't bring himself to follow them, but still admitted that they were (probably) right. However, there is an endless sea of people who disagree with what they mistakenly believe those teachings to be.
Humility is the beginning of wisdom. If you don't have the former, then you won't get the latter.
I find that most people in cases like this choose not to believe something for the simple reason that they don't like feeling as if their lesser impulses, or perhaps even the things they've done or would like to do, are immoral. So they say "that's stupid," "I don't believe that," and really don't even try.
There is also a great difference between what the Catholic Church teaches, and what many teachers and books say the Catholic Church teaches. Many a soul has been scuttled by bad teachers. Don't let yours be among them.