I think a spying app in his phone is the best way to catch a cheater or prevent cheating on you.
I hate cheating.If you want to use a spying app I recommend you to use spytomobile. It is really stealthy. When I thought my ex girlfriend (I tried to be straight in my past) was cheating on me I installed it on her phone. I could read her messages, see her call history and see her location. I read that an unknown person with name Julia offered my ex to come to her and try new silky bed sheets wich she had bought. My ex answered she would come to her in 20 minutes and typed a sex smile at the end of message. Using spytomobile I saw where she was. I jumped in my car and came there. I saw them through a window and there was not any girl with my girlfriend. I saw a black guy who was fucking my girlfriend. I became mad on her and took a baseball bat from my car. Then were scream, tears and blood.
I used spytomobile and it was helpfull. If you don't like it there are plenty of such apps