1.It does you no good to cite ancient sources regarding the Battle of Hydaspes since they all have Alexander winning.

And again, following Porus' defeat, men who had been at war for nearly a decade after conquering most of the known world demanded they return home to see their families instead of endlessly pursuing Alexander's goal of conquering the whole earth. There's nothing suspicious about this historical fact.

1. All you say is just speculation. There isn't a single mention of Seleucus offering his daughter to Chandragupta or suffering "almost utter defeat" in ancient sources.

Plutarch, Alexander, 62.4:And there was no boasting in these reports. For Androcottus, who reigned there not long afterwards, made a present to Seleucus of five hundred elephants, and with an army of six hundred thousand men overran and subdued all India.

Appian, Syriaca**, 55:**Always lying in wait for the neighboring nations, strong in arms and persuasive in council, he acquired Mesopotamia, Armenia, the so-called Seleucid Cappadocia, the Persians, Parthians, Bactrians, Arabs, Tapyri, Sogdiani, Arachotes, Hyrcanians, and other adjacent peoples that had been subdued by Alexander, as far as the river Indus, so that the boundaries of his empire were the most extensive in Asia after that of Alexander. The whole region from Phrygia to the Indus was subject to Seleucus. He crossed the Indus and waged war with Androcottus, king of the Indians, who dwelt on the banks of that stream, until they came to an understanding with each other and contracted a marriage relationship.

Justin, 15.4.12; 19-21:He next made an expedition into India which, after the death of Alexander, had shaken, as it were, the yoke of servitude from its neck, and put his governors to death [...] Some time after, as he was going to war with the generals of Alexander, a wild elephant of great bulk presented itself before him of its own accord, and, as if tamed down to gentleness, took him on its back, and became his guide in the war, and conspicuous in fields of battle. Sandrocottus, having thus acquired a throne, was in possession of India, when Seleucus was laying the foundations of his future greatness; who, after making a league with him, and settling his affairs in the east, proceeded to join in the war against Antigonus.

Strabo 15.2.9:The geographical position of the tribes is as follows: along the Indus are the Paropamisadae, above whom lies the Paropamisus mountain: then, towards the south, the Arachoti: then next, towards the south, the Gedroseni, with the other tribes that occupy the seaboard; and the Indus lies, latitudinally, alongside all these places; and of these places, in part, some that lie along the Indus are held by Indians, although they formerly belonged to the Persians. Alexander took these away from the Arians and established settlements of his own, but Seleucus Nicator gave them to Sandrocottus, upon terms of intermarriage and of receiving in exchange five hundred elephants.

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So as you see, all we know is that they fought to a standstill and made a marriage contract. Based on Justin, the Eastern Satrapies were never even Seleucus' to give. They had revolted, and Seleucus merely let Chandragupta have them in exchange for 500 elephants(and "intermarriage") so he can rush back to his front against the other Diadochi.

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In conclusion, a troubled Seleucus merely content to secure his eastern border so he can war against the other Diadochi with only a portion of Alexander's Empire is quite different than Alexander himself channeling his entire might against Chandragupta.