Is it appropriate to try to be friends with my ex again... 4 years later?

I was in a relationship with a guy for 2 years when I was younger (the relationship ended a little over 4 years ago) and it ended pretty badly. I was just beginning college and interested in someone else (who he happened to hate), so I gave in him the boot in the most immature way possible: a text. I'd heard that he was heartbroken and, for the next year, he tried to talk to me constantly and I ignored him. The next year, we would see each other at parties and pretend we had never met. Slowly, we began to talk again.. light, conversational topics that did not even imply that either of us remembered being together. It felt nice to talk to him again because he's hilarious/a good guy. We are pseudo-friends now.. commenting on each other Facebook statuses here and there. He recently posted a very long, heartbreaking comment about his girlfriend (an old friend of mine) breaking up with him. I would like to be there for him because he was such a big part of my life years ago and I miss his friendship, but I am not sure if it's appropriate.. or if it ever will be. I have been thinking about sending him a message about how I am available to talk to but I don't want him to get the wrong idea or be disgusted that I would want to help him out after what I put him through. The amount of time that has passed makes me wonder if it's appropriate, too.. we have both moved on with our lives and grown apart entirely. I am engaged and living in a different town and I have no interest in going out with my ex again.. will it seem that I am trying to do so if I get into contact with him? Is it appropriate at all?