SPOILERS
You have to get allie killed (go to the mall with her and make her answer the call) then block mark, don't answer the door when he knocks then you should be able to go to allies funeral, once you do that go home with Adam. Hope this helps!!
ALSO SPOILERS
I only ever had Rebecca as a partner, since I haven't played Mark's route yet, but does Mark also kill Allie when he gets jealous or is it Sebastian that kills her? I thought Rebecca only attacks Allie (which gets Allie killed) and Mark only attacks Adam (which makes Adam quit his job) on the « cheating route », 'cause I could never get Rebecca to beat up Adam (kinda fucked up to say with no context LMAO) even if I made Adam answer the call when we're hanging out at the arcade.