Be careful not to "biologize psychology".
Nothing you said is "false" but neither is it anything close to a whole picture. Psychologists, especially the ones who get noticed have a troubling tendency to grandstand and claim that they have unlocked the SECRETS OF THE MIND and to hell with everybody else. The reality is much more involved, much more.... messy.

What it comes down to is the fact that your mind is not your brian. To use oxytocin as an example: people use a synthetic version of this opiate endorphin as a pain management medication for cancer every day, but do not form attachments to everything around them (ie, the oncology nurse) because the context is not condusive to the formation of that mental construct. It is more true in psychology than any other field that just because every time you find A you also get B that A causes B. It is just as likely that B causes A, or that some other C causes both A and B. It is very possible, and a primary argument of other branches of the field, that happiness causes the endorphins to flow, triggering changes in the body to support the various things that can make us happy, and to take advantage of non-stressful time to repair the body. The reality is probably a cycle between the body and the mind, something of an opposite to the viscious cycle of depression: a vivacious cycle of joy, with the mind telling the body "I'm happy" and the body saying "I feel great!" and the mind saying "That makes me happier, and want to keep doing whatever i'm doing".

I suggest that you look into Maslow and Jung for some perspective on this stuff. Human beings are animals, but we are much more than animals, something psychobiologists and behaviorists choose to ignore, to their ridicule and our disservice. They have their uses, to be sure, but they are not what they claim to be.

In Christ,
~CSL