If that's the case then for me it's immoral maybe not from the eyes of human but definitely in the eyes of God. Actually, the moment you broke your marriage is already a huge sin, what more if you not only left yout partner but also find a substitute for her. What such a disgrace.
There are ways to break marriage without actually committing a sin, from the Church's point of view. That's why annulment process is possible, though it may be costly to prove that your marriage was made in a wrong way.
Orthodoxy is way more strict on that, until recent time it was almost impossible to break a marriage without being banned from church. But times are changing, and Orthodox Church has introduced the same procedures as well.