Am I insecure for being a bit upset that my boyfriend (21m) made our anniversary the same day as him and his ex’s?

My boyfriend (21m) and I (20 f) met over a year ago on tinder. We weren’t very serious at first (we had both just gotten out of relationships) and actually had a bit of a rough patch in the beginning but got through it. After around 4/5 months of seeing each other we got a bit more serious and I joked around and said “what are we going to say when someone asks how long we’ve been dating?”. He tells me just say a couple of months and I replied what about our anniversary. He suggests that we make one up and I agree thinking it’s harmless. He suggests September 1st. With our anniversary around the corner I ask him why he chose that day, to which he replies “that was me and my ex’s anniversary”. I obviously get a bit upset and ask him why he would do that. And he says I knew he wasn’t over his ex when we started dating and that he wasn’t in love with me when he chose it. He also told me it’s just a day so it shouldn’t matter and that I only care because I’m insecure and that I shouldn’t be with him if I think he’s such a bad boyfriend. He also told me it’s my fault for asking “ a stupid fucking question”and accused me of trying to set him up so that I could be angry. Attacking my character and putting words in my mouth. I also want to add that I didn’t yell at him or get an attitude a simply addressed that it made me upset when he tried to change the subject. He offered the change it but the way he reacted really turned me off. It feels like he doesn’t care enough to give us our own special day. It’d be one thing if it was a coincidence or if he didn’t care about anniversaries, but he insisted we make our anniversary a big deal because it’s important to him. I think every girl wants to feel special to her partner. The situation and how he reacted makes me feel like he’s subconsciously trying to relive his relationship with his ex. Am I overreacting?
Am I insecure for being a bit upset that my boyfriend (21m) made our anniversary the same day as him and his ex’s?
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