I have done that too way back before when I was 19. I really enjoyed the first moments when I was able to read his messages without him knowing but after a while, I realized that being continuously being up to date with his life and what's going on with him had me hanging and suspended while he had a good time with his life without me... it was because i did not move on... I have deprived myself of the opportunity to move on...

The important thing with breakups and being cheated is that you don't dwell in it... seek ways to move on and make use of your time doing productive things for yourself.

Learn to forgive and forget and to move on.. after all, he's not worth a single second of your time and any of your efforts after what he has done to you...