whom have I in heaven but thee? - literally, "Who is to me in the heavens?" That is, There is no one there that in my love for him can be compared with thee; no one who can do for me what thou canst do; no one who can meet and satisfy the needs of my soul as thou canst; no one who can be to me what God "is" - what a God "must" be. After all my complaining and my doubts there is no one, not even in the heavens, who cant supply the place of "God," or be to me what God is; and the warm affections of my soul, therefore, are "really" toward him. I feel my need of him; and I must and do find my supreme happiness in him. What would even heaven be to me without God? who there, even of the angels of light, could supply the place of God?

And there is none upon earth that I desire beside thee - That is, Thou art all-sufficient; thou dost meet and satisfy the needs of my nature. All my happiness is in thee; no one on earth could be substituted in thy place, or be to me what thou art as God.

Psalm 73:25 Parallel Commentaries

Of a Low Estimation of Self in the Sight of God
I will speak unto my Lord who am but dust and ashes. If I count myself more, behold Thou standest against me, and my iniquities bear true testimony, and I cannot gainsay it. But if I abase myself, and bring myself to nought, and shrink from all self-esteem, and grind myself to dust, which I am, Thy grace will be favourable unto me, and Thy light will be near unto my heart; and all self-esteem, how little soever it be, shall be swallowed up in the depths of my nothingness, and shall perish for ever. …
Thomas A Kempis—Imitation of Christ

Covenanting Adapted to the Moral Constitution of Man.
The law of God originates in his nature, but the attributes of his creatures are due to his sovereignty. The former is, accordingly, to be viewed as necessarily obligatory on the moral subjects of his government, and the latter--which are all consistent with the holiness of the Divine nature, are to be considered as called into exercise according to his appointment. Hence, also, the law of God is independent of his creatures, though made known on their account; but the operation of their attributes …
John Cunningham—The Ordinance of Covenanting

Cæsarius of Arles.
He was born in the district of Chalons-sur-Saone, A. D. 470. He seems to have been early awakened, by a pious education, to vital Christianity. When he was between seven and eight years old, it would often happen that he would give a portion of his clothes to the poor whom he met, and would say, when he came home, that he had been, constrained to do so. When yet a youth, he entered the celebrated convent on the island of Lerins, (Lerina,) in Provence, from which a spirit of deep and practical piety …
Augustus Neander—Light in the Dark Places