Why do guys act like they dont care?

Im just looking for some perspective on this. Basically, my ex cheated on me with 3 girls, it totally destroyed me when I found out. I tried to move on but nothing really helped.. I did some stupid and regrettable things and went on a downward spiral. Months later he got back in touch with me and said sorry for what he did.. eventually we got talking again and ended up trying again. Things were fine apart from the typical arguing over me not trusting him, thinking there were more girls, etc. But apart from that we were really happy, we felt like the bad things that had happened had brought us closer together and that he really wanted to be with me. Then he decided to randomly end it via text message... This has really messed me up because it seems like I had to give so much to try again and have so much willpower to forgive him and try to be with him and not feel ashamed.. its like Ive been led on and lied to. And everyone said that they were surp rised because they always thought it wouldve been me who wouldve ended it. So basically what Im wondering is, this guy is totally emotionless, he always says he "isnt bothered" etc and acts like he doesnt care... which is really hurtful because it makes you want someone more if they act disinterested in you. And its also really heartless to tell someone you love them etc then the next day be like ah well Im not really bothered. it just makes me feel like Ive been totally used and lied to again.. that he can easily discard me this way. So why do guys do this? Is the reality that they do care in some way but they dont wanna show it? or does he genuinely not care and Im just clinging onto some false hope? the reason Im asking is that people have told me things, such as him saying (when we were together) that he loved me and cheated on me was the biggest mistake of his life etc.. but a part of me feels like this was just to get people to feel sorry for him or to convince everyone else and himself that he cared when he really didnt. I was also told that when we had only just started talking again and hanging out, we spent a day with his friends and after I left he pulled one to the side and told him that he better not try to **** me and to back off.. when the guy hadnt even been remotely acting this way at all. So if he didnt care and isnt bothered then why did he do this? or is it a case of I dont want you but no one else can have you? I dont know, I just find it very odd that guys put up this guard of not caring and acting like they arent bothered.. I dont know if its to seem 'hard' or 'manly' to their friends but it doesnt make sense to me. Maybe Im just too emotional to understand feeling nothing haha..

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