Most Helpful Guy
You've accomplished more than me, props. As for your question, ask yourself this: 1) Do you still like your ex enough that it could jeopardize your current relationship? 2) Is your new toy the jealous type? If "no" is the answer to both, I see no reason why not, but be aware, lots of guys think boys and girls can't just be friends (which sucks for everyone).
Most Helpful Girl
Just because two people Break up doesn't mean they can't and don't Make up and that it's Good-bye, my love forever. And with an "EX" who Obviously still Marks an X in both of your hearts, with a newbie who has come along, you sometimes find that you are this monkey in the middle when it ends up to Be------I'm talking to my ex boyfriend.
I am sure the new boy in town doesn't Think there is any monkey business going on, trumpetplayerforlife, but it could lead down a bad beaten path, should it Continue where you and the "Ex boyfriend" are 'Talking' a bit more for the other's own liking and he could go bananas later on.
Keep That part of your life with the Ex very lite and almost no sweet at all. You have moved on now, you have someone else and the Ex must realize that He and you cannot have your cake and it two, it will end up to be a War of the Roses in the end with your new friend.
Good luck. xx