You said, you don't have problem getting laid. May be thats the problem. You can stop getting laid, and show her your feelings are genuine. Just don't over do anything. Keep it natural and take it easy.
treat her like a girl mate, and be really caring towards her. dont treat her as if she is only good for a shag, treat her like a lady, wine and dine her, open the doors for her, just be a real gentleman. good luck mate. i hope it goes well for you.