What could be the reason for his sudden change in attitude?

My ex and I were in a long distance relationship for about 3 years. Things ended badly because I had moved even farther and I met someone new. After about 1 year I contacted him again and apologized for like the hundredth time and we decided to try and be friends (the whole relationship we were basically best friends more than lovers anyway) and I knew it wouldn’t be easy but I have been very patient.

We didn’t talk often, only on each others birthday or on a holiday and have a short conversation of how we’ve been doing. He was always very cold although trying to be nice and didn’t open up much about anything at all. I gave him space and it’s been now 3 years since we broke up.

Last time we had spoke was on my birthday in September and he seemed a lot nicer than before and we talked a lot more too but didn’t speak again until today because it’s his birthday and the way he responded completely surprised me!! He said he wished he had seen my text sooner because there’s a lot going on and he wants to tell me all about it! He also said he wants to videochat or call since he doesn’t want to tell me over text (which is weird in him! He’s always been an introvert so he doesn’t like to videochat or call). What could be the reason for this sudden change?
What could be the reason for his sudden change in attitude?
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