Jerking off with your girlfriend's BFF

You, your girlfriend, and her best friend Melissa were supposed to have a movie night at your place, but unfortunately your girlfriend couldn't make it, so now you and Melissa are alone. She's wearing a cuddly sweater and cute fuzzy socks, and, with just the two of you hanging out, the two of you find yourselves in a flirty mood. With the sexual tension is ramping up, Melissa lets you know that she doesn't wanna betray her best friend... So she suggests the next best thing: the two of you jerking off together with her fuzzy socks. That's *not* the same as cheating, right?