Boyfriend problems

So me and this guy have been seeing each other since November. Everything was great until like a week ago. I was never sure about his feelings for me so I didn't know we were in a relationship. We got into a argument because he saw me hanging out with another guy that he doesn't know. He's a friend of mine and nothing more than that but he doesn't believe it. He took me out for my birthday on the 26 and I guess that's when my guy saw me with him. He's also mad because he forgot my birthday and feels like it's my fault for not reminding him. I've never given him a reason to not trust me and i dont know how to even handle this situation because I didn't see it as a problem and I thought he trusted me more than that. I talked to him yesterday and he keeps saying I'm playing games and that he didn't even want to talk to me anymore. I want to talk to him in person because I feel like that's a better was to communicate but he's not answering my texts. Can you guys give me any advice on how to handle this or share similar stories if you have them? I really like this guy and don't want to lose him