Roman History 03: Valerian's submission and Gallienus Betrayal?

Rome has had it's downs in history especially during the years of chaos. A moment within this chaos that really did make me wonder was of the kidnapping of Valerian. Valerian ascended to the rank of Caesar after Gallus and Aemeilian. He decided (the senate more like) to share the throne with his son Gallienus to help control the massive stretch of land that the empire consumed. I believe this was a fair and honourable move on his depart.

Things however did not span to well for Valerian as he was captured by Shapur I (second Sassanian king) who carved out a nice sum of land from the Romans. Valerian now being a prisoner of was and the first emperor to ever be in this situation sent shockwaves through Rome. A time where such news would not comfort the population as instability between the praetorians/ army and senate had been ongoing for quite some time. Never the less was Gallienus forced to turn a blind eye to his father's capture or was it great being an independent emperor where his father would hold primary judgement?

This is the question I ask myself as I do think it is an adequate reason that Gallienus did not pursue Valerian because of the recent break away state (Gallic empire) formed by Postumus. The Gallic empire enveloped Gaul and Britannia which were valuable province to the Rome. This like I have stated is a very serious threat to the roman nation but a feeling of mine does make me ponder the idea that Gallienus discarded his Father to Shapur I as I am sure there could have been a generous exchange possible for Shapur I that never occurred. Do not get me wrong, I know emperors before him had committed much more serious monstrosities even Caracalla but for some reason this situation shocked me when I was ready "The history of Rome Rise And Fall" by Stephen p. Kershaw

So Gallienus was his son ready to pounce and betray his own father or an emperor who had the best interests of the empire at heart over his own family?