What makes an ex change his personality and his mind over night?

My ex keeps changing his personality and I’m totally lost. I’ll start at the beginning. We met at work and were flirting straight off. he is a couple of years younger than me but that was never a problem. He puts so much stress on himself that he shouldn’t. He finishing a uni course and he has a year left. So he has the stress there. He is basically a lackey at work and takes on stress of a manager that he isn’t paid for and gets no respect from any of the people at work even though management expect him to do the role of the manager on min wage the same as the rest of the staff. He also is stuck living at home cause he can not afford to get his own place. He doesn’t get on with his whole family and doesn’t drive and has to rely on his family to get anywhere as he lives in the middle of nowhere. so he had all this stress on him. he had this from the start to which he even got nose bleeds when he got really stressed.

Our relationship when we finally got together was great. He was my first boyfriend and my first everything. We spent time together and were so happy for 6 months. One day he mentioned to me his mate invited him to london but he wasn’t going. When I asked him why he said cause his mate was a girl and didn’t want to make me feel uncomfortable. I said don’t be silly and go have some time in london with mates to stop being so stress full. He went and basically came back a different person. I went a week without seeing him when he came bk cause he made every excuse not to see me. Then on the sunday after he said we could go for a meal monday night and then spend all day tuesday together as we both had the day off. I was so excited all that monday as I’d not seen him in over a week. I met him and he basically while used the excuse we never spend anytime together and we’ve drifted apart. We parted then I talked to him the next day and I asked him how long he hasn’t loved me. he said he still did. Eventually we decided to be friends but 3 weeks after we split up, he is now in a relationship with the girl from london and goes down there once a week. (we live in the midlands). He kept ignoring one min and talking like a best friend the next. So indecisive. I sent him an email saying I was fed up of him messing me around and we will keep it work colleges. He didn’t contact me so I started to get my head sorted. the the next time I worked with him, he was following me round like a lapdog constantly watching me and never taking his eyes off me.

The problem I have is other people getting involved. His best mate at work who he idolizes, is a player so I wonder if he swayed him away from me. Also I’ve found out that a friends boyfriend has been “advising” him a week before he dumped me.

any ideas what the hell is going on? my head is fizzled cause everyone I talk to has a different opinion, that I have non of my own anymore.