In the end...

Up to interpretation, but I believe he called his buddy to let him know he’ll confess everything tomorrow.

His wife Patricia who had just left him.

Up to you. I figured it was his wife.
The symbolism of him walking out into the daylight seemed to signify going towards something better, a better, brighter future. Calling the partner would not have aligned as much with that symbolism as calling his wife. Also the emotional support and comfort that he clearly needed at that point would not have come from his partner, but rather his wife.