Would u be mad if this was u?

Me and my boyfriend have been together for almost 9 months but recently in the summer we split up for 2 weeks bc I had family problems. In the 2 weeks we were split up one of those days were my birthday. My boyfriend never said happy birthday to me and I found out recently he was with another girl the day before my birthday and the day of my birthday at 9:30 in the morning. When I said something to him about it he said they did nothing but talk and they are just bestfriend. Well rewind to November when she texted him while we were at my grandfather's birthday party and he said that she was some girl he had just met he never said anything to me about them hanging out in the summer. This isn't the first time he has lied to me. So when I went through there messages on snapchat she had sent him a "tomorrow is national couple's day" post and it said "send a ❤ if u miss them" "send a 💛 if u love them" and "send a 💙 if u think there cute". He sent 3 💙, 3💛, and 3❤. When I asked him of they dated or talked in the summer he said no she sent that as bestfriends. I dont know if he is telling the truth he told me nothing happened between them but I dont know if i believe that at all. He knew he had messed up so he unadded her on snapchat. Well today she texted his phone asking why he did that and he said bc he was gonna get rid of snapchat but ended up keeping it (which isn't a lie he was gonna delete his snapchat but I convinced him not to). I dont know what to do am I crazy for being mad at him for not telling me or no since we were broken up? (keep in mind while we were broken up we were still texting bc we both really like each other)