Finn is Force-sensitive and it shows best in his healing abilities, which he's figuring out more or less on his own, with some remote consultations from Luke and Rey. He's VERY good at it, very popular in medbay and a great help to everyone.

Poe has horrible migraines (stress, recent injuries, aftermath of torture, reasons are up to author). They're so bad they actually impair his ability to fly, so in addition to feeling physically ill he's also miserable and feeling useless and medication isn't helping that much. Finn knows he could help, but considering Poe's last experience with someone using the Force on him it probably wouldn't be a welcome suggestion. That is, until Poe himself asks Finn to help him.

++ cuddling and hair stroking and forehead kisses
+++ Finn gets a little misty-eyed at how readily and completely Poe trusts him with something he's had terrible experiences of
++++ happy end. The migraines don't magically go away all at once, but Finn's intervention helps a lot and Poe is soon back on his feet
+++++ seriously, forehead kisses, I have such a thing for this and I would love you forever for including them