There's a demon inside of me. Can I kill it?

Hello friends. I have begun a new relationship, but because I am in such a transitional period of my life, I initially compartmentalized it into a very specific role before it even started: "practice." I went looking for a suitable partner for the purpose of adding another notch to my belt, knowing full well that I would move on in time. But this girl that I have become enamored with is too sweet. I sincerely enjoy her company and being around her (trust me, this is rare). She makes me happy, and I make her happy. I haven't giggled this much in years. It's the most comfortable start I've ever had. And I feel like a fucking asshole.

How can I deactivate my own conspiring mind and just... be? I am tired of over-thinking everything that I do. I would like to just ride this one out without doing a cost/benefit analysis of my every move. Any advice?