It is rude to deceive someone you have relations with.
Lori has been dating Ben and Tom at the same time, without either Tom or Ben being aware of each other.
Lori wants to take the next step with Ben.
Lori lets Tom down gently before asking Ben to be official.
Lori asks Ben to be official while continuing to text Tom in secret.
Ben agrees, and Lori is happy to have found the one.
Ben sees Lori's texts with Tom and breaks up with her.