My ex followed the one ex I always felt insecure about after our breakup. I don’t know how to interpret it.

I need some honest outside perspective because I feel like I am too emotionally involved to see this clearly.
My ex and I were together for about a year and four months. Our relationship became very complicated toward the end. We broke up and got back together many times. There were a lot of arguments, jealousy, insecurity and emotional reactions from both of us.
I know I was not perfect. I could be jealous and impulsive, and I know some of my behavior pushed him away. He eventually told me that he was tired, unhappy, had lost respect for me and did not want to continue the relationship.
The confusing part is that even after saying these things, he would still be affectionate with me. He would hug me, kiss me, tell me he loved me and sometimes act as if he did not completely want to let me go.
Recently, however, he became very firm.
He told me that this time it was 100% over. He said we were no longer together and that eventually we should remove each other from our lives. He also said that if it was easier for me, we did not have to do that immediately and could wait a month or two.
Then I noticed that he followed his ex.
And this is where the situation becomes difficult for me.
She is not just some random ex.
She was the ex he had the hardest time getting over before me. They ended their relationship but remained on good terms. At one point after their breakup, he tried to get back together with her, but she was already involved with someone else, so it did not happen.
Later, he met me and we became a couple.
Now, after our relationship has ended, he has followed her again.
I know that following someone on Instagram does not automatically mean that he wants them back. I understand that.
But knowing their history makes it difficult not to wonder if there is still something there.
Especially because of the timing.
He just ended a relationship that lasted over a year, after months of going back and forth, and now he is reconnecting with the person he previously tried to get back.
Part of me thinks he is simply moving on and that I am giving one Instagram follow much more meaning than it deserves.
Another part of me wonders whether, now that he is finally free from our relationship, he is looking back toward someone he never completely stopped caring about.
I also keep thinking about whether I was simply the person he loved after her, rather than the person he ultimately wanted a future with.
I do not want people to tell me that he will definitely come back. I also do not want people to tell me that he definitely wants her back.
I genuinely want an objective opinion.
Given their history, how significant would you consider this follow?
And more importantly, how do you stop yourself from obsessively checking what your ex is doing after a breakup?
I know I need to accept that the relationship is over. I am just struggling with the possibility that he may already be looking toward someone else.