Do you think he's cheating?

My boyfriend had a girl texting him the other day and i asked about it and he said he let his friend use his phone which is normal but the way he acted when i asked was not. Also we both agreed to not have facebook and he had a Facebook messenger notification the other day. He again said a friend downloaded it to talk to his girlfriend but then he deleted it before i could even look at it... Then today he fell asleep and i was playing on his phone taking pics and everything but when i clicked on the internet app a site about "blue waffle disease" came up. I looked in the history and he was looking on multiple sites about that and aids. He is the only sexual partner ive ever had, however he has had multiple partners before me. He was checked before he got with me though because his ex cheated on him. I don't know if he's been with another girl or if it was another one of his friends. I looked up the symptoms and i don't have any so i don't know why he would look this up. I haven't asked yet because i want to have everything figured out before i start drilling him but im scared. this man is the love of my life and i don't want any of what has been going through my head to be true.