Is it wrong to consider dating other girls whilst knowing that if this one girl asked I'd jump at the chance, although I know that she'd never ask?
Dating other girls or boys for that matter is always somewhat tricky if you have strong feelings for another person. If the girl has not shown an interest in the past or the present it is likely that she won't show an interest in the future. My advice for this would be to build the courage and talk to her about your feelings. Explain to her how you feel about her, hopefully she has similar feelings to you and you can progress. But if she doesn't have the same feelings as you, I encourage you to try and move on.
Maybe give yourself a little bit of space away from the girl and on your own to come to terms with your feelings and to somewhat get over the girl, before then moving on and meeting new girls. As cliché as it sounds there are plenty more fish in the sea. As hard as it sounds now, there can be another person out there who you may have mutual feelings and fall madly in love together. Never stop believing in love... it's a powerful thing!