AITA for asking my friend with a brain tumor to pay me back $750 in rent after he found a subletter?

I (26M) live with a now close friend “Tom” (34M) in a 4 bed 2 bath house along with "Jemma" (25F) and "Anna" (28F).  Anna’s Visa was rejected in January when she tried to come home from abroad and since she is unable to make it back to work she can’t pay her share of the rent. She did find a last minute sub-letter but Tom rejected them for being too last minute and not included in the choice.

For context Tom is the only one on the lease, Jemma and I have subleases, and Anna isn’t even on a sublease because Tom never requested a new long term lease (was supposed to be done months ago). 

While all this was going down Tom found out he has a benign brain tumor, is in his last semester of grad school, and understandably stressed about money and the possibility of not being able to work during his surgical recovery.

Because of the rough patch he’s going through and because he’s a friend I offered to loan him $750 for the empty room until it was filled even though I’m not obligated to do so. We only had a verbal agreement that he’d pay me back when he could.

After just two weeks of searching Tom found a subletter and charged them $1000 a month plus a $500 deposit so he’s now making an extra $250 a month on the room. She also signed a sublease agreement.

Once the new subletter paid her prorated rent ($750) I asked Tom if he could pass that back to me since the vacancy was filled and we could settle up. 

That’s when the convo got heated.

Tom asked if he could keep my $750 as a buffer for the next few months because he now realises that he’s the only one on the lease, won’t be able to work during his recovery, and the “subletter could leave at any time”. He basically argued that since he holds the long‑term risk, is going through a very vulnerable time, and Jemma and I won’t pay beyond our subleases, he would like to keep my loan as a safety net, even though the room is paid. 

I pushed back and said that if the subletter leaves we’ll deal with it then. To me the $750 was a bailout for the month to take the pressure off of him not a long term donation and as of right now I’m the only one in the house down any money. When I didn’t give him the answer he wanted he immediately became more passive agressive towards me and borderline manipulative which has still left a bad taste in my mouth that I’m trying to get over.

We did cool off and hug it out afterwards and he agreed to return the money but I still feel conflicted. On one hand he’s dealing with an incredible amount of stress and I am finacially able to help him  I don’t want to be the guy demanding money from a friend who has a brain tumor. On the other hand, I feel taken advantage of since I helped him even though he got himself into this mess, he’s going to be making extra money off the sublet, and he tried to justify keeping my loan on top of that as a safety net. 

AITA for asking for my loan back from a friend going through hard times when I have the means to help?