Giving my key back

My fiance and I broke up. We've had a hard 2 weeks where we got ourselves in stupid arguments which was because we both our in defensive all the time. So one day after i left our place to work. I work away and come home weekends. (Just until the end of the year) thats when I was going to go there for good. So one day when i.lefr there he was upset about me calling stupid a night before but he forgot that he was very mean and i just reacted but well... he never talked to mw for four days then i got a texr saying he wants alone time permanently. So i found out he met a girl in the day he decided no talk to me. Was much i confronted him he doesnt said nothing about that. But i do know there is something between them. Just don't know how much. So.i went there and gave my key back. Altought all my stuff still there. I will pick up as soon i fix a place for myself. I dont have space at ny job where i stay during the week. I consider it what he did cheating and he doesn't. He was my best friend of 7 years. He saved from my last relationship where i had to found out my bf of 2.5 was getting married with someone else while being witj me. And he saved me from this hell. We have been together for a year. He got arrested witj dui and possession because partyinh to much and i bailed him out. I was patiente and we finally start doing better. He left most of his old habits. I used to complain and the long distance made hard with my trust issues. He had a dui back in january. And now hes with that girl that just turned 22 (we 26) that has a dui. And doesnt work. Probably like.bad stuff as well. And I am a good.woman. work hard. Always helped him and his family so did he helped me. I am just so confusing. Was i right giving the key back? Is he a cheater?