Search Results: never turns out like you want it to

Recently I have been under an incredible amount of dispute with my friend. This is the situation, my friend let's call him Eric, has another friend, let's call him Yusuf. Well, basically what happens is that Yusuf is like retarded and he constantly annoys me, to what degree you may ask. Well, he often steals things from my bag or puts things inside, such as rocks. For instance, on time he even put sand in my water bottle filled with water. Every time I confront him, he just laughs and says it's not a big deal. Across these two years, every three weeks I would go up to him and tell him (in the face) to stop and it's not funny. However he just says it's funny for me and does it again. You may think y make a big deal, well imagine having that done to you for at least three times a week! He usually takes my stuff or puts things inside my bag whenever I have my back turned making it extremely annoying. He usually does this when I talk to my friend Eric who sees Yusuf take my stuff or litter my bag when I face him. However, he always refuses to tell me before Yusuf leaves or when it is too late. Considering that we have been friends since year 7, I have never been mad to him. However, the thing which happened on Monday completely made me not want to talk to him. Basically what happened was that I went to the toilet and put my bag right next to his bag and pleaded for him to keep it safe, he nodded and said ok. When I was going to the toilet, I saw Yusuf stalking me, at first I thought he was going to go but he just looked at me go in, I was busting so I couldn't really do anything, I did tell him to fuck off tho. As soon as I locked the door and took the shit, he just banged my door, and chucked my bag in the toilet next door. I saw it as he legit showed it to me. I felt betrayed and angry to a degree I don't know what to do with the two. I could easily bash Yusuf up but by doing that Eric would hate me. I don't know what to do, should I maintain the friendship or not