Ex Boyfriend, Sexual Tension, and Cheating.

My ex and I were long term high-school sweethearts who broke up about 10 months ago because of the distance of our relationship (1000 miles due to grad schools). We still harbor feeling for each other, though mostly affection, and both of us are planning on staying friends and have come to terms with the way our relationship works now, and he even has a new girlfriend of 7 months (who is insanely like me and who bothers me to a GREAT extent, but that's not the point).

However, over the last couple of months, we have both begun flirting a bit over chat, particularily when one or both of us are tired or when he's been at a party (I don't drink due to alergies), and recently our late night "discussions" have become extremely intimate. Both of us feel a bit guilty about this, but there is just a lot of sexual tension floating around, whether it's discussed or not, and when we're not at our best (tired or drunk) things get expressed that shouldn't.

The other day, he proposed an idea which he believes would help with the situation: next time we're both home on break from school, we should get together (secretly) and have one final and terminal fling to get all the excess sexual tension "out of our systems". He says he's aware of the moral implications, and he's not sold on the idea either, but he feels that the emotional infidelity and sort-of cheating that happens, often on his part, is worse because it's ongoing, and getting everything done and overwith might be a better moral decision.

I have no idea how to respond to him. We had a discussion about it on Skype, just to get ideas out in the open, and we've decided to both consider it for a while before we make any choices, but I have NO frame of reference for this kind of thing. I've always held cheaters in extreme contempt, and it's a little distressing to me that I'm even considering this sort of thing, but the way things are working between the two of us right now, for lack of a better way to put it, just doesn't work, and i value him as a good friend too much to lose him over this.


So my questions are thus:

Which is more moral, if one or the other has to happen: little to moderate ongoing flirtations from a boy who I care for deeply but who is is a relationship, or a little nightime get together, as it were, that is a one time thing?

And us this something that would even actually work, so that we can "get it out of our systems" and go into a clean friendship? or would it do more harm than good?