I have this strange habit where when things start getting good in the relationship, I push them away

When we start to feel safe in a relationship subconsciously we will re-create past experiences in which we were hurt and that need healing.  If your pushing those you care about away its likely you experienced being abandoned or disappointed in someway by those you depended on for security leaving you to believe it was your fault and not good enough as you were. By pushing those you love away your daring them to prove yourself right while hoping they will stay and validate that you are lovable and good enough.

It is said it takes 100 “at a boys” to undo the harm cause by one person saying your not good enough so its likely you will continue to test people in this manner until you make this fear/false believe conscious and doing so take ownership of the story you have been telling yourself with regards to love and being worthy of being loved.