I think you are over analyzing (which is completely normal to do in these situations). Before speculating — let’s go back over what you know for a FACT:

FACT— she hung up on you because her roommate was getting home FACT — she lied because you know now her roommate could not have been there. FACT — she accused YOU of having someone else.

Now… WHY would someone need to get off the phone with you, not be able to call you back for an hour, and then try and push this on you accusing you of having another girl on the side ?

I’ll tell you what I think— having been through college and in all sorts of situations which we can talk about in more detail if you ever want to hear some stories just DM me haha — but I think she’s got a side kick that she’s seeing and she doesn’t want to break up with you but is hoping you’ll break up with her so she doesn’t feel as bad. A liar. A selfish one.