Can a man really change?

So my boyfriend is a liar and sneaky to boot... we broke up over it multiple times now... the last time we were apart for 3 months and I started dating someone else. Which he knows about. We ended up back together. He claims he's changed but because he lied so much in the past I no loner believe anything he says. So can a man change if he knows he can lose the woman he loves if he doesn't?
Can a man really change?
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