Before today, I would have said that the following objection to Aristotle and Aquinas' view that our actions should always have our happiness as an end is fatal: Surely it is permissible to do something good for someone solely in order that they receive the good; granted, such an act is a virtuous act, and hence a component of happiness, but it need not be done for the sake of one's happiness.
I now wonder if the following isn't a good answer. All virtue is a form of love. True love is not literally selfless. It includes unitive, benevolent and appreciative aspects. The unitive aspect cannot leave out the self. To act in love requires, among other things, that the lovingness of the action be a part of one's intention. Thus, the true lover does not merely bestow a benefit on the beloved. The true lover bestows a loving benefit on the beloved—a benefit that not only is intended to benefit the beloved, but also to bring one and the beloved closer together. This is what keeps the love of neighbor from being a cold philanthropy.
It goes similarly with virtues that are subspecies of love. When one does a kindness for another, one does not merely intend that a kindness befall the other, but one intends to do her a kindness. In a genuine intellectual community, one not only intends that the other should come to believe a truth that one takes oneself to have, but one intends to share the truth with her. When acting in courage, one does not merely intend to stand firm, but to stand courageously. In each of these cases, the exercise of the virtue itself enters into the intention. In fact, in each case, what one intends just is a particular case of the exercise of a virtue. A consequence is that "the exercise of virtue" is a success term. If one does someone a kindness or shares the truth, then a kindness is done to the other or the other receives the truth, respectively. Now happiness is multiform, and each form of it is an exercise of a virtue. Hence each virtuous actions involves precisely the intending of an exercise of a virtue, and hence is the intending of a facet of one's happiness.