How do I feel better

I have been w my bf for four years and things are going okay. A couple months ago he blindsided me and told me he wasn’t really happy anymore with me like he used to be. And broke up with me. Not even an hour after he said he’s made a huge mistake. We’ve been working on things and he says he’s back to being happy with me but I think from that experience I lost a little trust in him and now with every time he’s a little colder or distant, I automatically think he’s not telling me something. He still says that was a huge mistakes and was so stupid of him but it really traumatized me to the point where I think about it everyday. I’m looking into getting therapy, but what I can do personally to just move forward and stop letting this terrorize my brain??