Cheating SO....need some advice??

I have been with my current SO for almost 9 months. He has now received 3 blowjobs and has had sex 3 times with the same girl. I love him and would love to spend the rest of my life with him. He says it's just physical and he is trying to get over it but it's killing me and making me extremely self concious. He says he wants me and only me and wants to build a future with me. He had mentioned taking a break but I just feel like that would hurt more because he would be with her. What should I do?? Should I move on??