Choice Between Two Men - What Should I Do?

I have been in a relationship with a good guy for the past three months. Prior to this we were friends for a couple of years.

We are very attached to one-another. He is very loving and kind and treats me with respect. However, I don't think he is the love of my life. There is something missing but I can't pinpoint it.

We are both aware that this relationship may not last for numerous reasons: There's a nine-year age gap, for starters. We are at very different life stages: I'm a 21 year old student while he's a 30 year old with a career. We both want to leave this city for different reasons: He wants to leave for a new job. I want to study abroad. So we may be separated by distance soon.

An old flame reappeared in my life recently. I hadn't seen or heard from him in nearly a year when he suddenly emailed and said he wants to see me.

We used to date, but not seriously, before he left to travel the world. He's the same age as me. He's the most adventurous and inspiring person I've ever met.

At the time I felt he was a great love in my life. I would have done anything to be with him. I still wonder how he is getting on today. When he left he told me to move on and meet someone else - so I did. But now he suddenly wants to see me and I'm experiencing a moral dilemma.

Do I stay with my current partner, who I am comfortable with but not necessarily deeply in love with, and reject my ex? Morally it feels like the right thing to do. But my time with my ex was unlike anything else. It was complete joy, elation and bliss. However, he is in the past.

I feel guilty for having these thoughts and don't want to make any rash decisions or hurt my current partner. Please can somebody offer some logical advice