Help me out , I know I’m not stupid

So lately my boyfriend seems to be distancing himself, being on his phone a lot more , and just being plain weird such as mood swings (one minute he is happy and next he is upset about something) . I noticed he’s been playing basketball which idc he’s taking care of himself but he makes remarks about his body which I can’t help but notice is weird because he usually doesn’t do that . He’s acting all weird , and is being lazy and etc. so either he is tired , or he might be cheating, I wanna go through his phone to check it out but also that’s not me to do that either . So help me out here ladies or gentleman