So I have a leather couch, but it’s very sticky. I have no idea why.
I just moved into this place, so this is weird. Obviously all leather is sticky to some extent, but this is exaggerated. It sticks to your clothes! It has a dull finish where it sticks to them an it is almost like an adhesive. What could I do to fix it?
Stop engaging in nookie on it? 
Okay, serious answer: sounds like a waxy buildup to me (not necessarily wax, but one with wax-like properties). If it’s true leather, pick up a bottle of leather-safe cleaner to remove the buildup, and follow it with a good long-lasting conditioner. Any leather store or leather goods store will be able to suggest brands. Check with the furniture place or the guys at the mall who sell the leather jackets.
If it’s fake leather of some sort, then you can probably get away with a mix of dishwashing soap (Dawn, Joy, etc) and water. Scrub gently with a sponge dipped in the mix and wrung out, dry immediately with a paper towel or dishrag, and apply a protective finish. I don’t recommend Armor-All because I don’t like what it leaves behind, but YMMV. Anything should do it, really, but I’d avoid anything with orange oil in it because that, IME, tends to contribute to the waxy buildup rather than removing it.
Saddle Soap is what you need. Available next to the shoe polish.
But let me get this straight, you are sitting on a previous tenanta sticky sofa? Ewwww, yuck and gross!
Ok, a bit of a clarification.
Fistly, it seems like real leather. If it’s fake then it’s pretty impressive, although it is very tight, so I could be wrong. Secondly, it seems to occur in areas where some part of the finish has worn off. It doesn’t seem to be something on top of the leather. I’m not totally sure though. Does that help at all?
That’s odd. Usually Crisco is slippery, not sticky.
Answer… meet username.
To the OP: it could be that waxy buildup I mentioned, or not. Regardless, cleaning (with saddle soap or with something else) is definitely in order. Personally, it sounds to me like someone used Armor-All on it at some time in the past, as that’s exactly the sort of residue I’ve found.
So, clean it.