Can i trust my boyfriend again?

I have been in a relationship with a guy for 3 years.Previously he was married for 19 years and is now divorced due to ex wifes infidelity. He has 3 children from his marriage the youngest being 18. Last night his ex wife stayed at his house when i asked him he said she hadnt, later i rang him and he admitted she had, he says because his middle child wasnt feeling well. He tells me they slept in seperate rooms but how can i believe that when he lied about her being there in thw first place.Im heartbroken please help