I need some help from some experienced people like you..

I'm 23 and since 15 March I've changed job. I moved to an another company (not too far away from the older one) because I needed to move on.

Since I left the older job, my ex-boss told me that he would like to have my help if he needed. I answered him with a: "I need to think about it".

After the last meeting (my last day) my ex-boss asked me some help every week.

I've answered him for some simple request, like: " I need some info on this project e blah blah blah"

Now he asked me to go to my older office to talk about an older project that I made.. I probably know that this time, this request is a big one.

I'd like to stop this circle, because I do not have time and I'd like to stay free of mind.. I know that I shouldn't answer him at the first request but.. This is the situation.

How I can stop him (in a good way) to make me this kind of requests?

These requests are not paid to me, but I don't want to collaborate with him anymore so I don't wanna his (eventually) "extra money".

It's my first experience (I've changed company just once) and this situation is a kind of " break up with my girl".. I do not know how to move.

Can you help me, guys?