Can girls forget hurtful things that their boyfriend does to them?

After my boyfriend and I got together, he and his friend had 2 girls stay the night with them at his apartment. He lied to me for 11 months telling me he never met them in person. The only way I know now is because one of the girls messaged me saying he was trying to get with her. He denies that, but he lied to me even after she told me that she stayed the night, not once, but TWICE. And he expects me to just forget everything.