My husband might be having an affair

So lately my husband has been acting real suspect about his phone. He never leaves it laying around even when he's sleep. He always has an excuse on why I can't use it. The other night he fell asleep & some random # called and hung up when I answered around 11:15pm. I went to look at his call log only to find he locked me out of his phone! 
However he always treats me like a queen and makes me feel like I'm his 1st priority. I've known his since I was 12 years old & he's never cheated on me. 
I don't know what to do or how to handle it. I don't want to accuse him of anything because I know nothing....for all I know he could be acting funny about his phone because he has a surprise for me or something....ugh I'm so confused