Bad Girlfriend

I have a boyfriend that I've been with 11months but for like 4months I've felt like he doesn't want to be with me. He doesn't give me any attention, we can not talk for like 3 weeks and he wouldn't care. I'm in love with him which is why I won't leave. But I'm also like in love with this other guy who I've know for so long and today we had sex. Like really good sex and I just don't know if I should tell my boyfriend or just move on with it.