Hello there. This is the second time I'm posting here, I don't like to do that, I don't like problems with commissioners... I'm looking for an advice because I'm not sure if it's the right thing I'm doing.

A fur asked me for a cooperation on a commission some time ago. That was quite ok, just a regular commission you'd say. He promised me to send some references but he forgot... for 3 times. Then I was busy and he didn't contact me. I thought he was no longer interested but then about a month ago he contacted me again. I was busy with Eurofurence and had no time for other commissioners at all. But I stopped accepting commissions meanwhile because of the university following in September.
This person (I don't want to cause any harm to him so that's why I don't just tell his name) keeps contacting me every day. He got somehow glued to me... (the "you're my good friend" thing) Every 3 or 5 days he keeps asking me when I'll have the time for him. I can't tell him because I need to focus on the university and have some other personals problems to solve than to do commissions. I asked him what the commission is anyway and he told me he'd be interested in about 15-19 pictures (BW, detailed.. a wall poster - omfg)... O.O I dropped my jaw and became frustrated. Then he asked me to be the next one. But since I'm fair to everyone and have already a few people in the commission queue for commissions I'd like to finish, I just had to tell him NO.
There have also been communication problems since his English is bad. I told him one thing and after 10 minutes he asked me about it again.
I'm very embarrassed about this situation but I feel uncomfortable with this person though he has done nothing wrong... o.o What do you think about it? Any suggestions on a solution? Please advise...