He lied

I found out yesterday that my boyfriend lied to me about not sleeping with someone else while we were broken up for a month. I feel so betrayed after giving him time after time to tell me the truth and he still didn’t out of fear I wouldn’t want to get back together with him. It’s hard for me to look at him and to be in his room after making this discovery, but I still love him after being together for a little over a year. He’s my best friend, and yes we were broken up when he did it, but idk how I should feel... he’s been so loving and doting and honest and loyal to me since getting back together, which is why it’s so hard for me to put aside who he was in comparison with who he is now.. I know nobody can decide how I’ll feel but I guess I’m just looking for some advice