My boyfriend had sex with his ex when we broke up and we have been back together for 2 months now he tells me...?

I love my boyfriend very much and he says he loves me and is in love with me and wants a future with me marriage , kids everything.Last night he told me when we broke up in the afternoon that night he had sex with his ex girlfriend because she called him for a ride and he went to her house and they had sex.I asked him when we got back together is there anything you need to tell me before I say yes to getting back together he said no baby I love you.I told him last night well you not going to talk to her again right? he said no way but if she needs something I will help her because I'm a nice guy I help everybody if they need it.I don't know should I break up with him? I am so upset and when we broke up I couldn't eat, sleep or anything I was so upset I don't understand how he could have sex with his ex?

BTW.. She is now friends with almost all his friends on Facebook & I'm not. Please help I have didn't sleep or eat since I found out.and today is our anniversary :(
My boyfriend had sex with his ex when we broke up and we have been back together for 2 months now he tells me...?
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