My now exDH was a chronic user for most of the 20 years we lived together. Cannabis is a tricky drug because while it does have significant long lasting impact on a person, its effects are subtle in a way that alcohol and other drugs are not. I also find that chronic users are convinced that because it is 'natural' that means using it is not detrimental, which has been further influenced by the legitimate uses of it and CBD for pain control or control of symptoms for a number of illnesses.
Personally I found that my ex's use made him disorganised, forgetful and moody. He spent a massive amount of money on it as well, which was always a huge bone of contention between us. Ultimately it was a way of psychologically isolating himself from relationships with other people; when he was high he was free of anxiety but that also meant he never dealt with the underlying causes of his anxiety. It distanced him from me and his children.
But it is important to point out that when people are chronic users, they do not get "high" or "stoned" in the way we think. Their brains get used to the drug and so while it affects them, they are not out of it or in giggly munchie land the way most of us were when we tried smoking in our teens. My exDH used to argue that he was not stoned and therefore cannabis had no real effect on him and it was fine for him to look after the kids, work, drive, have dinners with our family, etc while he was under the influence. The obvious question then is, if it has no effect on you, why smoke it? He never had a good answer to that.
I found it very difficult being married to someone with a cannabis addiction because unlike alcoholism or heavy drug addiction like cocaine, no one takes it seriously. Although we probably would have had problems in our marriage regardless, his cannabis use made it impossible for us to have a meaningful long term relationship.
Obviously this is all my personal experience and I don't have any studies or whatever to back it up. But I would just say that if you have a partner whose cannabis use is affecting you and your relationship, you have a good reason to be concerned and don't be fooled by those who say that it is somehow different from all other drugs.