I already told you Tyrael is a jerk of an older brother. Inarius loves him to death (he would die for his brother if told to) and is always trying to get the other to just smile or something at him. Thus, a lot of trying to prove himself goes on, which generally ends with little bro in trouble, and big bro rather pissed. At one point, Inarius tries (and actually does) to outfly angels much larger, stronger, and older than him, but ends up crashing, and shattering his spine. This is kindof a breaking point for Tyrael. Should I go on? Give more detail?
So Tyrael is the Archangel of Justice and Such. He hasn't learned how to love yet (no family unless you count the council- but the there's Imperius. Eyugh) Then, out of the blue, A seraph is delivered from the arch, and every one claims this is his little brother, Inarius. He realizes they're right, and now he's got an energetic little ball of light who looks up at him like he's every thing there is, and ever will be. This doesn't go down with him, as he finds Inarius distracting at best, the way he is always bugging for attention, and getting into trouble, Inarius on the other hand, just wants his big bad archangel brother to teach him how to be as big and bad as he is, then they can go end the eternal conflict together (Inarius is very young at this point- like a little five year old or something.) Tyrael does not agree. More?
Little brother! Inarius has a serious case of brother worship going on. Said brother had no time for Inarius, and would tell him off almost every time approached. Things like nightmares, getting shoved around by other angels (their are bullies everywhere, even in heaven) or needing advice were met with the same reply: deal with it yourself. Tyrael didn't want to admit that he had no advice to give, as this was out of his experience. Inarius tries to do as his brother tells him, but is often met with failure. He is not strong enough to fight his demons on his own yet. As he gets older, the inability to get Tyrael's love leads to Inarius becoming reckless, foul tempered, and kind of like a mini Imperius, minus the spear, reputation and general ability to back himself up. With no where to turn to, young Inarius decides that what he needs is a shield. remember that pick where Older!Inarius has his hands raised to the sky? well, Inarius starts working on his shield at about age nine human terms.

Then I really don't know. Although, Lilith did say she still desired (and hated) him right before he banished her.