The penis has a lot of momentum, You are breaking their hearts every time you say no, but only because of the expectations. Purity and being sensible like you is also hot as fuck, imo will make you more interesting. Just let them know you like to get to know people slowly, that you really dont want to have sex right away, but you would really like to spend some more personal and comfortable time with them in private. As a guy the mentality going in is going to be different and probably much better for you, theyll be trying to just enjoy it as well on the same level as you know, not just seeing how they can move on to sex. I mean, they might still try to get with you, but then its more like flirting than a disappointment.