You're mixing up your Girls. Ai chan is dateing salarykun and yes its heavily implied that they are sleeping together, but she isn't preggers in the Pre-serialization. Its the Student Council president who ends up preggers with the Sensei that she spent 3 years pursuing, but their relationship doesn't start until after she graduates (although she does trick him slightly to win their "bet" by changing the time on her phone from 11:55pm to midnight so she can get him to express his feeling before she graduates since he does it before the end of the day).