Bella Thorne is making improvements in the guy department by picking guys like Charlie Day over Scott Disick ... this according to Charlie Day.
We got Charlie arriving at LAX over the weekend where he told us he'd actually heard about Bella tweeting she wants to marry him -- and while he seems genuinely flattered ... there's an issue: Charlie's wife.
The 'Always Sunny in Philadelphia' star makes it pretty clear the 19-year-old actress can forget about a menage a trois -- even if she keeps going out in see-through tops.