Can someone really change

I've been dating this guy on and off for a few years now. He's 34, and I'm 28. We decided to give this whole relationship thing a solid try and have been officially monogamous for about 5/6 months now.

Some woman has been posting online that he's a cheater, has a fiance, has women in every city he travels to for work and now other women are claiming he's psychologically, emotionally and physically abusive.

These women are claiming this behavior has been ongoing since high school, so about 20 years of cheating, controlling, and abuse.

I've never seen this behavior from him. I've never seen him get angry. He's never raised his voice and has always been sweet and super respectful to me. He's never pushed when I say no.

I've asked about the fiance and he said he broke it off before we started dating. Said the relationship was over a long time ago but needed to wait for the lease to expire before officially ending it. Said there was other women when we were just talking and he's cut contact when we went official.

So do you think someone can really change this dramatically or am I being played by a master manipulator