When should i give up on my ex?

I met a guy at work who I dated for 4mths. I had never felt so sure of anything in my entire life and he said he felt exactly the same until his crazy ex started to follow us around on Valentines, obsessively call and text and pop round while I was there. She offered him � to sleep with her and said he could live back at his old house rent free. When things became tough at work, he became distant, quit and had no money so went back to her for a mth. He started calling after a few wks saying he'd made a mistake and we tried again for a wk but he decided to break things off while he got his head together as he was confused about what he was feeling. After another mth apart, he calls & txts me, we meet up in clubs when I'm out with friends, he visits late most nights and has said he still doesn't know what he feels. He's shown me scars on his legs she caused and he tells me he fells guilty for leaving her, still likes me but doesn't know what he feels for her? Should I walk?