If you're trying to grow in purity, I would not recommend that you talk openly with your boyfriend about your temptations. While it's helpful to be clear about your standards and the boundaries of physical affection, there's no need to pour out your personal temptations. Doing so will only cause the both of you to think about them more frequently.
Imagine if you experience a particular temptation that he does not. After giving him this information, the temptation will not leave you. Instead, it will be transferred to him. Often, these discussions about temptations are just a spiritual cover-up to have a sexual conversation. To avoid this trap, talk to a priest, youth minister, or family member who you trust.
In the meantime, remember the words of St. Josemaria Escriva, who wrote, "Never talk of impure things or events, not even to deplore them. Look, it's a subject that sticks more than tar. Change the conversation, or if that's not possible, continue, but speaking of the need and beauty of holy purity--a virtue of the men who know what their souls are worth." He added, "I have never talked about impurity. . . . But I have spoken many times, as I have to do, about chastity, purity, and the joyful affirmation of love."
. St. Josemaria Escriva, The Way (New York: Scepter, 2002), 41.
. St. Josemaria Escriva, Christ is Passing By (New York: Scepter, 2002), 52.