Most Helpful Guy
that's too much,
don't reply nor give him any kind of attention, if he really wants you back then he would find better ways to make up to you, avoid him, see if he tries again, if you genuinely feel like he means it then the choice is up to you at that point, if he stops trying after 2days of getting ignored than he obviously doesn't mean it.
however though, if that was me i wouldn't go back with him no matter what.
Most Helpful Girl
This is up to you and what you feel would be the best choice for yourself.
Personally, I wouldn't waste anymore of your time on this guy. He's taken advantage of your heart, and of the relationship you both once shared. He was seeing someone else on the side, and never had the decency to grant you a reason for breaking up
I wouldn't be there for him anymore. Don't bring stress to yourself or further commit your time to someone who's not willing to provide you with the same commitment, effort or relationship back. The following / unfollowing is probably just for attention, so you will notice him and he can stay active in your mind.
Move on, and let your ex remain in your past. Focus on yourself and making yourself happy. If he writes to you, i'd just delete it and block him if it were me.
Sometimes removing someone permanently from the social sites you use each day, can benefit you too, as you're not constantly seeing their stuff, or being reminded of the hurt this individual has caused.
I hope you move forward and feventually find an amazing person who will treat you SO much better soon.