My boyfriend is a hoe

I've been with my boyfriend for six years we've had our ups and downs like any other couple and it has taken a lot of forgiveness to even get to this point but recently I was contacted by a girl saying that my boyfriend is her "boyfriend" and saying they've been sleeping together for six months and she never knew about me because he would always lie to her and tell her I'm a crazy ex. All of this going on while me and him live together. I'm at the point where I am absolutely done; but I cannot shake this feeling of me wanting to kick his ass I am livid. I know the adult thing to do would be to go high and walk away but right now I'm ready to go low and bring the chaos I feel so disrespected. I don't know what to do I'm tired of arguing about it I just want to hurt him like he's hurt me emotionally. Am I wrong?