He unfollowed you because he wants to move on more efficiently. But a better question would be - why do you care? It's his personal life now and it does not concern you at all. Move on and stop stalking him pretty much.
You unfollow them, because its part of the steps to moving on. When you hold on to things they gave you or you have with them, it means you have never moved on from that relationship. And it becomes extremely unhealthily. It means it's one, over. And he wants nothing more of you or a part of you. In the end you don't need to be constantly reminded of the past. Because then you will never be able to move forward in life. It will hold you back. Ignoring post is not enough. You have to get rid of everything. Get rid of pictures uploaded, delete them on other devices, clothes, items, jewelry, toys, whatever must be put out and/or burned. What is done is done.
But jumping into another relationship just after you ended one will give anybody the wrong impression that they just been used by use. Wither physically or emotionally. Usually it's emotional.
Stop playing stupid. You know he unfollowed you because you already broke his heart and now you’re pretty much showing off your life without him? Do you expect him to just watch you date other guys and show yourself off after you left him? Kinda rude.
I think he should delete and block you all together. You sound kinda crappy.
It's is because he wants to move on and whether he said he feels spark or not seeing posts of you on dates will give him some slight jealousy. Unfollowing you will just help put things in the past and if he doesn't see the pics it won't provide any unnesessary negative feelings.
I think it's cos he doesn't wanna know what's going on with you and doesn't want to be a part of your life anymore. So instead of having to just ignore your posts like what you said, might as well just unfollow... Kinda like severing ties.
Because it shows that you have moved on and it has ended between you two! Specially deleting pictures you had together! One day you'll find the guy who will want to show you off and never break up with you