Why is she still married?

Ex P is with OW for over 2 years now,she left her hubby quick and they moved in together after 4 months.Yet she is still married to the father of her kids.But she announced everyone she is engaged to her soulmate lol.How can you be engaged when you`re not even divorced?

Im European so i was just wondering if this is normal in the States.Or is divorce so expensive in Massachusetts?If she loves him so much,how come she is not divorced after 2 years?