Au contraire he has plenty to gain! He was found out and about to be deported. If not for the OP he'd be back in his home country where apparently people are incapable of earning a living wage, so much so his relatives constantly have to beg for money or 'starve'. If that was true he'd be basically condemned to death by going back. Anything is preferable.
If what you said 'not much gain' is true that doesn't put him in a good light either. It means he's lying about his relatives as his home country offers at least enough prospects for him to survive despite what him/his family's claiming that money is urgently needed. If he could do it don't see why they can't.
You talking about him going for someone 'not very rich' again what other choice did he have? I highly doubt that there's a queue of women waiting to date someone like him. The bar is set really low on MN for 'good' men but there are plenty, my own husband has cleaned up my sick, dealt with issues etc multiple time and he's a good provider. There's much better out there.
The OP doesn't want more from him. If you read all her posts they are good on 33K household income with no young children (son at uni but that's temporary).
The MAIN cause of OP's financial issues and stress is him sending money home. And that's what's raising alarm bells. What your husband does is irrelevant, if you've got enough and are happy to send home fine but OP and her DP don't. If they did then she wouldn't be stressing about it to the extent of her 'MH being greatly impacted'.
Regardless of scammer long game or otherwise this issue has to be nipped in the bud.