Feel bad for wanting to have send outside of marriage?

My friend is very religious and I am to, but I'm more so on the "carefree side" of the spectrum and I really love my boyfriend and I want to have sex with him. Personally, I think it's a natural thing that happens, but she sees our relationship as nothing but lust. I however don't see it that way, we both truly love each other and have been together for a year and a half, but she says it's the "devil trying to lead us into temptation." I'm a firm believer in God, but I want to share that with my boyfriend, is this bad?