Why can’t I let go of the hurt/past? Why am I bringing my past problems into my new relationship?

It can be difficult to let go of things that have hurt us in the past. There is a biological reason for this. Our brains try to protect us by making sure that we look out for situations that have been dangerous in the past.

To your brain, the difficult experience of being in a toxic relationship was dangerous. It caused pain, physical or emotional (sometimes both), and put your central nervous system into a distressed state. So, in current and future situations, your brain remembers that it should "protect itself" by using the same actions or words that were used in the previous relationship. After all, you survived the incident, so your brain thinks you did pretty well!

While our brains have been wired to protect us based on past information, this isn't always helpful in the modern world. If you were chased by a bear as a cave-person and you escaped by running away, when you see a bear again, you run! Your brain learned that this is a good way to protect itself, so it continues to do the same thing. However, many of the things that cause our brains to perceive danger are not actually dangerous in the modern world. So, this adaptation that has kept us alive can also have negative impacts on us when applied to modern day situations, like relationships.

While running from a bear is a good idea, running from a healthy conversation with our partner is usually not such a good idea. However, in the same way that your brain can learn to run from a bear, it can also learn to disengage when conversations become difficult. These conversations could have been perceived as dangerous- even with a safe partner, and even when the conversation would benefit us.

Our brains aren't very good with context. Without intentionally evaluating your communication patterns and where they come from, you might become stuck reacting not just to what's going on in your current relationship, but also to what has happened in your past relationships. 

In order to change our patterns in relationships, to "let go", we need to identify where the behaviors and habits that impact your relationships are coming from. We need to determine what happened in the past to lead to specific behaviors, and with that knowledge we can begin to change our actions and words.