cheating???

My boyfriend of three years is cheating and he don't know that I know cause I went thur is phone and saw everything. I only went thur his phone cause he was acting different! I been acting like I don't know cause it hurt so bad. So in 3 months I plan on moving out while he at work! Then I'm gone out him on my block list cause I always give him a chance to be honesty with me. I'm print the messages off so he know why I left. This is going to be so hard cause I love him we even have matching tattoos! What should I do? Any advice?