How do i forgive him after sleepin with someone else?

I'm 28years old and i'm in relationship with guy who I thought was great. One night about 4months ago he slept with tart behind my back, he says he loves me and I believe him as the woman he slept with is out the country and she won't be back, she wasn't going to tell me that he cheated. He confessed to me a couple of nights ago and told me he wanted to be honest and that it meant nothing. He also told me if wanted to marry me, he got ring too. I ended up locking my self in the bath room for 2hours. I mean he's perfect, works as gp, he always kind to me, funny and charming, plus he is fit with great body and I genuinly believe he loves me. The night he told me ended with him on balcony of his flat naked. The reason being is cause he couldn't get into toilet so he pissed over the balcony and I locked him out. After me shouting at him that all if cared about was his fancy car and his money he ended up taking his clothes off on balcony and I mean everything boxers as well and threw them over balcony, before that he threw is �15000 diamond jacob and company watch over too along with his car keys. I mean that watch means the world to him. After that he started beggin me to open door on his knees naked. I ended walking out flat leaving him there as there were tears in his eyes. He never cries. He was left on balcony for 4 hours weather is freezing. I went to my friends that night for the four hours and she said dump him and she said he was tryin to toy with my emotions. I ended up going back to let him in and He started tellin me he loved me and he wants me to be his wife. I stayed strong and told him to pack his bags. It's his flat. But he left. He now keeps sending flowers and apology cards asking for me to forgive him. I love him. What do I do? how do i let him into my life again as I feel like I am going to forgive him. What do I do? I'm confused. I don't have much family, actually I have none, my family are all a bunch of users. He was the one who would always be there for me when things weren't good. He's supported me financially and he swears he loves me and if wants to marry me. I would have married him without thinking about it before he told me if cheated. I love him. What do I do? He is staying at a friends just now. Plus I get constant texts from him saying sorry. How do I bring him back into my life? How do I punish him so if won't do it again?