Here is what happened:

On Tuesday, my roommate and I go to a bar, a HB9 and her friend HB8 come back to our place, two blocks from the bar, the HB9 (my target) met my roommate before. My roommate goes straight to his room with the HB8, I stick in the living room, going up to C3.
And BOOM, first disaster : they start texting each other, my girl go check on her friend, she comes back. Things start again, but half an hour later her friend come in the living room and state that they have to leave, 10 mins later I get my girl's number and walk them to their car.

I have no more hope so that makes me better on text game, they agree Thursday to meet us at an other bar (one with booths).
We have a lot of fun in the bar, lot of teasing, gentle make out, back to the house. My roommate go to his room in 5 mins, it takes me 10. I makes sure her phone stay in the living room. Back to C3. And she decides to check on her friend, that time I react : I go in his room, the girls are on the bed, not him, I start some fun with them to keep them from talking, re-escalate and bring back my girl to my room. Escalation to early S1.
And BOOM, second disaster, her friend knock on the door, wants to talk to her, my girl wrap herself in the sheets and go talk to her. She comes back and we go further in S1, I hit her with almost every LMR prevention that I saw on PUAForum.
And re-BOOM, her friend rushes in the room and states that they have to leave. 15 min later I'm walking them to their car. It was their last night in town, I tell my girl to call me when she's back in town, she says to shout her 2 or 3 messages and that we will definitely see each other when she comes visit in 3 weeks.

My roommate says that both time his girl left, they were talking when she suddenly decided to leave (and he was indeed dressed up).

So I'm wondering :
Why did they isolated themselves so much (they also did it every time we arrived to our place and made some private references at the bar). How can you prevent that from happening?
Is that a known girl behavior that I'm not aware of?
What would a MPUA have done differently?
What is up with the HB8, why did she come back on Thursday if she freaked out on Tuesday (except maybe because my roommates pays for whatever a girl can drink)?

PS : HBs were 21, my roommate is 28, I'm 23

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Learner PUA
Sorry for the english, I moved in the US recently