They should be friends and allies, and we should treat both of them as such.
If Cruz wishes to be a friend and ally to Trump, he will drop out as soon as he is eliminated from first round contention, throwing his support to the frontrunner...but he will not.
Instead he will cling to the lifeline afforded by the archaic selection process, in the mistaken belief that he will beat the opposition, and Trump will not...and in fact, if that is the GOP objective, both Trump and Cruz will be bypassed in favor of Kasich, who polls far better...
That depends on how loyal he thinks his delegates and Trump's delegates are. I'd rather have as many loyal Trump/Cruz delegates as possible. If Cruz drops out, around half of his votes will go to Kasich. I do not want a Kasich surge that makes the pro-Amnesty governor look like a legitimate convention choice.
I'd also rather see Trump beat Cruz at the polls and in delegates and earn a first ballot nomination. But Trump is a little shaky on the political campaign process. It's better for him to learn in the primaries so he's as ready as possible for Hillary's corrupt political machine. Cruz creates the need for Trump to build his political skills, and that is a good thing.