My now-husband and I experienced this same thing. We were young and we really wanted to have him come to the US, see how he liked it, live with me for a bit like a normal couple, etc. before taking that next step. But, as you already noticed, that doesn't exist. I knew him in person already and spent time in his country. He applied and received his B2 visa, came a few times and spent a few holidays with my family, and then we had to make the decision---marry or break up because we couldn't do this forever. We ultimately decided to take the chance, do the K1, and get married. We have been married 6 years now and we are very happy with that decision, but I totally understand the hesitancy! Good luck!