Relationship Issues

My boyfriend has been talking to some girl on Snapchat and I just found out they talk on the phone every night or FaceTime every night!๐Ÿ˜ก๐Ÿ˜ก๐Ÿ˜ก๐Ÿ˜ก๐Ÿ˜ค๐Ÿ˜ค๐Ÿ˜ค๐Ÿ˜ค
I have no idea how to confront him about this, he's flirting with her and I think it's because he's so bored with me. Our 6 year anniversary is on Saturday and I don't know what to say to him. He's been so weird for like 2 months and he's very protective of his phone and doesn't really talk to me or show his love for me in any way, whether it's just saying I love you or giving me a kiss or being a gentleman. I deal with anxiety so just the thought of having to talk to him about this makes me have a panic attack. Please help!!!