My boyfriend cheated me?

I am engaged with a man and planning about our marriage,while I'm with him at his parents house I caught him that he is cheating on me with other woman.He has a text mate and even asking her to give him a photo,nevertheless,he even pretend with her that he has no girlfriend the way he talks.In the texts mages the woman asked him..where are you and what are you doing right now?? and my boyfriend said nothing I am just in bed and feeling bored.But, for god sake how could he say that such a thing to her which I am with him in his house.We had fight about it that moment.Then again after a months I discovered him that he is cheating me.We were having appetizer at the coffee shop when his phone rang..then he cant answer his mobile phone.then again we had fight.I dont know how can I trust him anymore..no matter what he does..I just cant trust him.