Sometimes we can't help but become attached to people quickly - its how we deal with this thats the issue. I don't think theres any reason for you to put a wall up but i think it is wise to be on your guard. Maybe explain briefly that because of previous experiences you feel more comfortable taking things slow and if he's a gentleman he will respect this and allow your feelings time to develop naturally. I think it would be a shame if you denied yourself this oppertunity but bare in mind that it is exactly this, an oppertunity. Once you've found the balance between maintaining your safety and getting to know this person better things will roll much more smoothly. Hope ive been helpful. All the best.