Not sure

I thought I was sure about having sex with my boyfriend. I've been away from him (out of country) for 2 weeks, so I've had the time to actually think it through without being influenced by how I feel when I'm around him, and I was so sure. But the I read something on staying abstinent until marriage, and while that was never what I had intended to do it did make me doubt that I was ready. I'm not sure how to handle this thing of being 100% sure one day and unsure the next.