Is my ball python constipated or something bigger going on?

I usually handle my BPs a couple of times per week, but haven’t handled Nico in about two due to business and him being the most friendly of my crew. I went to hold him today and realized that he looked thicker than I remembered, then noticed a dark spot by his vent and like, puffiness/fluid buildup? I think that would be the best explanation. I have him soaking right now but should I be worried? He’s been
eating perfectly fine and seems otherwise healthy. Husbandry is on point. Is it just sausage butt or should I try to get in with an emergency vet?

Some puffiness just above the snake's vent (aka cloaca) usually means he's about to defecate soon- not necessarily that he's constipated.

Often handling the snake will "inspire" them to defecate (especially if you're wearing good clothes, preferably "dry clean" only ;) ) but also, a supervised "swim" in shallow lukewarm water (NOT deeper than the snake's body height- like 1-3" max) in your bathtub will also help "get results". If you feel a hard lump just above the cloaca- like a marble of any size- that might be a urate "stone" blocking the way, and that would be reason to see a vet- to help your snake defecate, but failing that, just be a little more patient for now. Doesn't sound like an "emergency" right now.
For future reference, before you handle a snake, it's a good idea to check for this "puffiness" to avoid awkward surprises. :rofl:

Lol I’ve been surprised many times but never caught any of my guys so full! He just defecated after a little soak thank fully. My roommate was stunned by how he seemed to halve in size ;)

:weirdface...."Oh what a relief it is." :tp: :dance: