The problem is he is expecting not to pay anything for last month's rent and is also expecting full return of security deposit. Basically, I will be out of one month's rent. He is saying that since he is not going to reside in the house, why should he pay the rent at all for that month. If I pay him the security deposit right away, can I still be sued for triple the security deposit + attroney fees?

Yes you could still be sued. However I would not expect him to win. With him leaving the country it also seems less likely he would still sue.