I don’t know how to feel

5 year relationship, we’re both 24. Porn has been a problem in our relationship for a couple years now but it wasn’t until about 9 months ago I told him I didn’t have any more room for it and if he watched it again he was basically ending the relationship. He has told me for 9 months he hasnt been watching and this morning I found out it was all a lie. He begged and begged me to let him prove himself and that it would never happen again and downloaded an accountability app and has said he will go to therapy. I want to believe him but I don’t know how to feel or how begin trying to move on. Does anyone have a success story or is it all just bound to come crashing down in lies and secrets?