Okay, the school and program is better at Purdue, despite Arkansas being "good".

You and boyfriend would be closer to family.

Knowing your advisor is "safe"; no reason you can't meet/know another advisor and, as scary as that is, in the long run might be better because it would take social/educational "muscles"; you would have to interact with a new person (which will help if/when you get a job/leave school) and the whole point of view and approach to teaching/learning would be different so you'd have to work your own how-to-learn/see muscles and they could be made stronger by the interaction with the new.

The money could be a difference; approx how much does it cost to live in Arkansas versus how much in Indiana and would that be a wash because either place would work or is the more Arkansas substantive and the cost of living Arkansas that much less that the comparison of the four would show a clear difference? I don't think that you necessarily want to be "working"/making a living yet as a student, you just want to be able to, as you have been? You will still be a grad student, not a full-fledged doctoral-wielding bug expert making millions so, money should still be viewed in light of that so you have something to really look forward to in a couple years?

Purdue cost-of-living
Purdue salary

vs.

Arkansas cost-of-living
Arkansas salary

Obviously you are not worried about the money as you feel either one will be a good decision.

That leaves only your boyfriend's problems with finding an Illinois job? Not really your problem but. . .

You move, he moves with you/on you looks for job
You move, he does not move with you

Either way there, you are paying for yourself/the apartment!

You stay, he stays, status quo is maintained; nothing "new" happens, no new growth.

Do you feel lucky, Punk? Well, do you? I would take the chances, join the Navy, see the world, etc.