Advice please.

There's a guy I really care for and I think he cares for me. I believe in saving one's self for marriage, but I don't know if I'll be able to say no if one of us pushes boundaries ie start making out and touching in naughty places. Next thing you'll know clothes will start coming off and you know what happens after that. How can I avoid the sexual tension getting to the point where inhibitions go out the window? Advice please?