The fact that everyone talks about how Mimi and Angel know each other should be enough to indicate it in the book, shouldn't it? The actors or director can do more non-textually to clarify their relationship early on, but it IS supported by the text.
The movie actually tried to fix a few of these flaws. As someone already pointed out, in the movie Mark says he is going to look for Collins, which explains why he comes back later only to leave again. The movie also shows us Mimi and Angel's friendship earlier, like when they acknowledge each other at the end of the title song (I think - it's been a while) and when she runs over to hug him at Maureen's performance.
Somewhat ironically, though, when a bad movie attempts to fix the flaws of a good show, it only serves to point out that the flaws are there in the first place. Especially when they don't go far enough to fix the flaws, or when the movie is not good.
Nothing matters but knowing nothing matters. ~ Wicked
Everything in life is only for now. ~ Avenue Q
There is no future, there is no past. I live this moment as my last. ~ Rent
"He's a tramp, but I love him."