is he cheating?

so my boyfriend is usually so open and honest with me and he'd tell me everything he does with who and when and i didn't even have to aske him to do that but lately he's not been doing that. he's been saying things like "with someone to go do something " and i feel like if i ask he'll get mad at me for falsely accusing him of this but just now he ended or facetime call to answer the phone for "someone" and he called me back to tell me he was going to do "something" i need advice should i chill out or should i out a cage around my heart?