SUBREDDIT: r/Advice
TITLE: [relationship] Worried about my other half's kik habits.
POST: Throwaway for obvious reasons. 
My SO and I have been together about a year now, we live together and have a great, healthy relationship except maybe I'm in denial here.
So the story goes, a few months back he developed this new habit of very obviously shielding his phone screen from my view whenever he used it when I sit next to him. A while after I first noticed this I caught a glimpse of the app he was using when he hid his phone. The dreaded Kik. No 22 year old guy in a happy relationship should even have kik! 
Now I'm not one for confrontation, (as you can probably tell by the fact that I'm posting here instead of talking to him.) so I let it slide, he has a huge twitter following and is generally friendly so I gave him the benefit of the doubt. 
He continued with the phone shielding until yesterday I saw a message pop up, from a girl while we were out And I know I need to do something.
Thing is, how do I approach this, I know he will tell me that it's totally innocent but I'm suspicious because of how he shields his phone. But would it be my place to insist he shows me the conversation?  I'm nosey and I'm insecure but I feel I have a right to know if I'm being told the truth or not.
I want to figure out how to bring it up, I'm sure he thinks he is hiding it well and I don't want the relationship over, even if he is getting dirty, (ugh) and I need to know if I would be crossing a line by asking to see the messages? 
I've got a lot of emotions regarding this, it's messing with my self esteem and I've stewed over it for so long that it's affecting my sanity. Please don't just recommend I talk to him, I need actual tips on how to start the conversation and stay emotionally controlled ( I cry ridiculously easily)
TL;DR: 
otherwise faithful and loving boyfriend is having secret conversations with a girl on kik, how do I bring it up and can I ask to see the messages?