I agree with everyone that you should call him!! The only thing is that it has to be for the right reason and with the right intent (i.e., out of concern and to wish him well, not to use a tragedy to work your way back in). I'm not at all trying to imply that you have the wrong intention... I just thought if it were me that is what I'd ask myself before calling. I don't think it would be fair to him to throw the whole "I know you are in a long term relationship, but I still love you" thing at him right now, because he is probably going through enough uncertainties (to me it's just not the right time, and I woudld see it as a bit selfish if it were me with an amputated foot and my X came to me with that). Please keep in mind that his sister may not know the extent of his feelings for the girlfriend, or his intentions to marry her. She has been there for probably alot more than you realize, in addition to the recent struggle, so I wouldn't think it easy for him to walk away from her -especially if she has been by his side during this difficult time. Definitely make the call, but you'll feel alot better if you get it straight with yourself on what your intentions are with making the call.
Also, one last thought... if he wants to hook up somehow, be sure his girlfriend knows, or that it is over with them before you do so, to save yourself alot of grief and disappointment. Also, think if you were involved with someone else now, if you think you'd still be having these feelings?
All the best to you. I hope it works out. If not, it may be that his memory and your paths are crossing for another reason, which is much less attractive, like learning something important about yourself on why the relationship really ended, or why you weren't ready then... which will somehow better prepare you for "thee right guy" who will soon be coming your way.