I am a figure buyer, but I'm very new to the hobby. I buy Japanese anime figures (some video game ones too) and have owned a little more than 50 of them, but recently I sold a lot of them and have two that linger around in their packages from me not wanting to cancel the order and risk the relationship I have with the website. So I can sort of see where you are coming from, but I'm not sure what kind of "figures" he buys since action figures usually conveys something that cost like $20 and you get it from Walmart...but my figures can cost $200 each (though I haven't spent that much).
Anyway, compulsion is a big thing with figure buying...or really ANY hobby. Actually, in shopping in general. So when I see a figure that is REALLY pretty or REALLY awesometastic-and-tota lly-expensive I do a few things.
I'll pass if:
1. Not from an anime/videogame/manga I have watched/played/read or have any other deeper interest in.
2. Own more than two of that character, has to be full scale figures..I don't count my smaller cutesy ones.
3. Price. I usually pass on things over $150 and if shipping is anymore than $30, it wont be part of my collection anytime soon. The overall value has to be worth how big it is/the quality of it.
4. I gave it the 24 hour rule.
I follow the 24 hour rule like clockwork. It applies to everything in my life and I have saved a lot of money/impulse buying on it. If I do it in the store, I give it the 15 minute rule. I think about it for 15 minutes and if I can't find it worth it then I pass on it and put it back.
Here are some questions to ask when considering something:
1. Do I need it?
2. Is it worth it?
3. Will I use it more than once?
4. Can I see my interest in it dying?
5. If I don't like it, can I re-sell it (applies to figures) for roughly the same price?
6. Is it in my budget? Do I have "free money" to spend on this? (consider bills, next time I get paid, if I'm ordering other figures that month, etc)
Those are just some questions, it really changes depending on what I'm buying and where. The 15 minute rule is more for outside-of-the-house shopping while the 24 hour rule is more of the online shopping (which I do a lot more).
Try to get him to think of things this way. With figures, their value basically decreases when you open the box/package but it kinda depends on what he is getting. I know that's true for japanese anime figures but for action figures the hit is a lot harder when you open the package so re-sell is almost impossible since anyone who wanted it the first time has it.
ANYWAY, sorry for the tangent. Yes, try to get him to do the 24 hour/15 minute rule and ask him to ask himself questions about his need/want for the item. Also, you might want to separate your bills from his if he is this irresponsible. I do enjoy buying figures but I do realize that I have a cell phone bill to pay and textbooks to buy.
You say he has a serious addiction to shopping, which I don't think is true. If he was addicted he wouldn't have much of anything and would most likely be still living with his mother because he can't afford to live on his own. I've seen addiction in progress, and having a relationship with one is hard. I'm not sure of his debt situation but my friend is over $50k in credit card debt because of her addiction. But if you think he has an addiction, there are support groups that can teach him better spending habit techniques.
Side note, I do think your title ran most of the readers away. "Molding" is an awful thing to try to do rather than make him more responsible. I do also think it's a bit wrong for him to promise to pay you to clean his apartment but he hasn't paid you. I'd stop cleaning if he wants to be that way...for any job, if you aren't getting paid then you don't work.
If he doesn't straighten up completely, I say you give him an ultimatum or let him know that if he can't become more responsible that you two can't be together. Maybe talk to his mom, too...if you guys aren't on bad terms.