I know you miss her but you need to give yourself some space to sort out your feelings. You say you don't have an interest in her but you also say you have butterflies in your stomach when you try to speak to her. It all comes down to are you feeling nervous about the group or about expressing your feelings? Sometimes love is a cruel thing, it really is. My advice to you is to sit down and sort out your feelings. Once you know what you really feel you can tackle it and move on. Try asking another girl on a date and see where it goes. Hang out with friends to distract yourself or take on a sport or a new hobby. Don't ignore your feelings, identify them and make a plan to move on.