Questioning your motives in what you're doing is a healthy thing, IMO.
There were plenty of times I snooped in my XABF's truck to see just how much he was consuming. I sniffed ever article of clothing of his to prove to myself that the odd smell I couldn't at first identify was in fact coming from him (later verified as a new pot smoking habit). At no time was any of this sleuthing healthy because as Smacked wisely noted above, it was all about proving him to be an addict and not about seeking a healthy way out of our dysfunction.
There have been so many stories I've read on here of spouses going to mediation or court with an addict spouse for divorce or custody and finding themselves trying to prove to a judge that there is in fact a problem with little to prove it. I would definitely get an attorney's opinion if what you are gathering would sway the court where you are. No sense wasting time and energy if it won't. In my state, I even know of video evidence being presented and being shot down because as incapacitated as the addict was at the time, if the behavior was not causing property loss or physical harm to anyone, it wasn't proof of anything but a single wild night.
You asked if gathering evidence is the same as obsessively snooping and I think you're in it for the right reasons. Heck, I even full out enabled my unemployed XABF by landing him a job 3 counties away from where I was moving to because it meant I could escape him more easily. We do what works for our health and well being, right?
Best to you!!
Alice