Objection 1. It would seem that the angel does not love himself both with natural love and a love of choice. For, as was said (2), natural love regards the end itself; while love of choice regards the means to the end. But the same thing, with regard to the same, cannot be both the end and a means to the end. Therefore natural love and the love of choice cannot have the same object.
Objection 2. Further, as Dionysius observes (Div. Nom. iv): "Love is a uniting and a binding power." But uniting and binding imply various things brought together. Therefore the angel cannot love himself.
Objection 3. Further, love is a kind of movement. But every movement tends towards something else. Therefore it seems that an angel cannot love himself with either natural or elective love.
On the contrary, The Philosopher says (Ethic. ix, 8): "Love for others comes of love for oneself."
I answer that, Since the object of love is good, and good is to be found both in substance and in accident, as is clear from Ethic. i, 6, a thing may be loved in two ways; first of all as a subsisting good; and secondly as an accidental or inherent good. That is loved as a subsisting good, which is so loved that we wish well to it. But that which we wish unto another, is loved as an accidental or inherent good: thus knowledge is loved, not that any good may come to it but that it may be possessed. This kind of love has been called by the name "concupiscence" while the first is called "friendship."
Now it is manifest that in things devoid of knowledge, everything naturally seeks to procure what is good for itself; as fire seeks to mount upwards. Consequently both angel and man naturally seek their own good and perfection. This is to love self. Hence angel and man naturally love self, in so far as by natural appetite each desires what is good for self. On the other hand, each loves self with the love of choice, in so far as from choice he wishes for something which will benefit himself.
Reply to Objection 1. It is not under the same but under quite different aspects that an angel or a man loves self with natural and with elective love, as was observed above.
Reply to Objection 2. As to be one is better than to be united, so there is more oneness in love which is directed to self than in love which unites one to others. Dionysius used the terms "uniting" and "binding" in order to show the derivation of love from self to things outside self; as uniting is derived from unity.
Reply to Objection 3. As love is an action which remains within the agent, so also is it a movement which abides within the lover, but does not of necessity tend towards something else; yet it can be reflected back upon the lover so that he loves himself; just as knowledge is reflected back upon the knower, in such a way that he knows himself.
Source: Summa Theologica (New Advent)