Hi Jason, your two line comment says everything and thank you for posting it.
It can be possible when you have anxiety and depression, and I'm not a qualified doctor, the need that someone new maybe the person to help you overcome this illness because they take a great deal of interest in you, so an affection may develop only until you find another person.
There are many reasons why this can destabilise a person and suggest you contact your doctor.
You have to understand if it was the opposite, where you feel deeply in love with someone but they decided to move on.
Stability, marriage, children and a house maybe something you are aiming for.
Hope you can please get back to us.