People, some misleading explanations have been offered here.
The son (per CC) is not the source/origin of the Holy Spirit, but merely a second cause because there’s afterall, just one essence- The Son does not have his own essence, different from the Father’s, so he cannot “originate” anything at all in the Blessed Trinity. Whatever he gives to the Holy Spirit, he necessarily gets from the Father. So
one source for everything in God is proclaimed unflinchingly by the CC- Just one.
For those who have not frequented the Eastern Forum, look for the thread titled
Filioque-Distinguishing the essence and person of the Holy Spirit,
forums.catholic-questions.org/showthread.php?t=619526
Many helpful explanations have been offered there.
The best summary is that the Trinity is like a spring-river-sea, where there’s only one source/origin (the spring)- and the sea (Holy Spirit) has two causes, because its water comes to it from the River even though the river gets it from the spring- One source/origin, two causes, three bodies. The Sea is
caused both by the Spring and the River, without either of which it would not be- That’s the meaning of
cause. That’s the best explanation I’ve ever found: Spring-River-Sea (And it’s patristic!). So the Son is cause of the Holy Spirit in the way the River is cause of the Sea, but not in the way that the source of the water (Spring) is.