"There's been a lot of speculation about every single girl I'm with and it actually does quite irritate me after a while, more so because it's a complete pain for the girls"

Prince William is expressing his disappointment with the amount of speculation that surrounds his relationships with women. He is most likely referring to the intense media analysis that follows him and his romantic partners. He is also likely referring to the negative effect that this speculation has on the ladies he is with. He is likely revealing his issue for the women he is with, as they are typically subject to extreme public examination and criticism. He is most likely expressing his aggravation with the reality that he can not safeguard them from this type of attention. He is likely expressing his desire for privacy and respect for the ladies he is with. He is likely revealing his desire for the media to respect his relationships and the females he is with.