I don't know what to do

My boyfriend is upset and I don't know what's wrong , a guy tries to add me on Snapchat and now hes acting like I did something with him and I barley know that person!! Please help , I've tried talking to him and he's ignoring me and he doesn't want to be near me or have me touch him 😞😞😞 I feel so down right now and I don't know what to do I've tied everything ; I even explain who the guy is and he ignored me and it's not my fault that the guy was trying to add me on there . I haven't talked to that guy in a long time and that's before I was in a relationship with my bf... please help

P.s my bf knows me and he always on my phone and so he knows I'm not looking for another so why is he acting this way ?