The three of them are in a loving, established relationship, but Rey and Finn are both Force sensitive so they have something more together that's clearly a very special bond. Poe on the other hand is about as Force sensitive as a potato. He doesn't mind. He's not jealous and he's happy for them, happy to watch them because they're lovely together. But sometimes he feels-- not left out, exactly. A little sad that this is a part of their relationship that's so completely inaccessible to him, that he'll never understand. And more, that he's reluctant to even try because the only time he ever experienced the Force was under Ren's torture and he's still terrified of it. But he wants so much.

Long story short, Finn and Rey are happy to help their completely Force-inert boyfriend experience the good, gentle side of it and start to overcome his fear. Force sex would probably be a bit much at this point, but Force cuddles are totally a thing, right?