Can people change?

I’ve been with the same guy since 2014 I was 21 we got married in 2016. He has cheated on me so many times. Recently he started turning off when he was active on Facebook and I started questioning again. He was in fact talking to anyone girl and was hiding messages. He has all passwords something else. He never has a picture of me or him on social media. He never wants to take pictures with me either. I feel at a lost. Unsure what do to. He said he’ll change and fix himself but can this behavior stop am I wasting more time. I never once cheated or ever talk to men the way he talks to other females. I feel like it’s my fault I’m not pretty enough, I have a lot of health issues. Just want to know has anyone been in this situation and what advice could help me?