Need tips for avoiding negative thinking

I've been struggling with low self-esteem and low confidence for many years, but the last months it has started to affect me more than before. Part of it is probably related to my porn addiction, but I think a lot of it has other reasons that I need to deal with in other ways.

Anyway, as part of my reboot, I've also started taking daily walks to clear my mind, especially when I feel a lot of urges. The problem is that during my walk, my mind starts to wander and I easily start thinking negative thoughts which then leads to more negative feelings and so on. It's becomes a vicious circle and when I get back from my walk I feel even more depressed and the urges to fap are bigger than when I left.

Do you have any tips for avoiding negative thinking? Or how to get out of the vicious circle once you started?

 

Thanks guys, I will look into mindfulness and meditation and give it a try. It's never been my cup of tea, but then again I've never really tried it seriously. Hopefully I will change my mind!