My girlfriend and I have had a long distance relationship for a few weeks. During this time, I have been hanging out in a circle of friends, where I met a person that I have not been able to stop thinking about. I feel a surge of excitement every time we meet, even though we have only ever hung out as part of a larger group of friends.
This, however, has given me enormous feelings of guilt, as my girlfriend is an amazing person whom I would never want to hurt, or would ever dream of being unfaithful to, and with whom I’ve had a 7 year relationship which is very stable and loving and healthy.But at the same time, I cannot let go of these feelings, or the fact that I cannot stop thinking about this other girl. It feels like I’m weighting something that is safe and stable and loving, against something that is new, exciting and thrilling, and I feel completely lost. As I said, I have never actually hung out with this ‘new’ girl alone, just me and her, nor have I received any clear signals that she feels the same way – it’s just a feeling I get (I may have misinterpreted something that isn’t there).
What if I give up a happy life together with a wonderful person whom I love and who loves me, for what could turn out to be little more than a short flirt (if that). What do I do?
LemonVibe 
You know what wears off in time? Those chemicals in your brain that give you the new love feeling. I would go see your long rearm girlfriend.
This isn’t an easy black-or-white answer, as you know. Your decision (I think) should depend on who you are. Let me ask you this:
You are riding a bus on a cold day when a fashionable, talkative girl gets on and sits next to you. She LOVES your jacket and offers you $50 bucks to trade yours for hers. Now, her jacket is a slim cut leather, clearly expensive and drool-worthy, but your jacket you’ve had for a long time. It’s a bit worn and aged (maybe a hole or two even) but it’s also comfy and smells like home. Arguably the other jacket might smell the same if you kept it long enough, but that other jacket might not even fit! You won’t know until you’ve already given her yours and accepted the $50. So? What do you do?
Take her jacket, shiny, new, and complete with $50? Or keep yours? You’ve already broken it in after all and, remember, it’s a cold day. It’s gonna suck if her jacket DOESN’T fit and you have to walk home in the cold without one.
Answer that question, then go back to your problem. The $50 is the adrenaline rush, the appeal of something new, but will ultimately be spent relatively quickly and is meaningless in the long-term. Are you willing to risk going home in the cold alone for the chance at someone exciting? Do you even WANT to when your girlfriend is so warm and comfortable?
Well? Which is it?