Is my ex being petty?

Me and my ex broke up about 3 weeks ago and were dating for 4 years. When he's around me he acts like he's great, when he's around our friends he upset and angry. Saw him the other day and he was asking me so many questions on what I've been up to and who I hangout with now, and flirting. He clearly checks my Snapchat often. He's been on social media a lot more lately too, posting things that would usually get me mad. I've been completely ignoring it. Is he trying to get a rise out of me so that I talk to him? Want him back, how should I procede?
Is my ex being petty?
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