OP, you should definitely meet her before you make any hasty judgements. If they were going to have an affair, they would have done already, wouldn't they? There are lots of elements of your account that make me wonder how compatible your lifestyles are. His suggestion that his friends are making his clothes smell of weed is the sort of thing someone would say to their mum not partner. Not sure i believe him myself.
I think you both need to put your partner first in a relationship but also respect their existing relationships. A new partner laying down the law about when i could or couldn't see a friend wouldn't work for me.
You seem to have lots of preconceived ideas about what this woman would be like if you did meet her, none of them positive, and although every new partner might have one rogue friend you don't instantly love, i think liking a partner's friends is all part of the deal. If he likes her and you really didn’t, once you have actually met her, obviously, i wonder how compatible you are.
You have described her as an adulterous druggie who borrows money and this impression has come from your partner. He thinks she's great, from what you have said and enjoys hanging out with her, and it did make me wonder if they have more in common than you and her.
Did he tell you she told him to stop going on about you as a sort of compliment to you? If not, it seems a strange thing to report. As you haven't met her, you won't be able to gauge the context.
I have some opposite sex friends who would tolerate me talking about a new partner for five minutes tops. Do you have any male friends? I think heart to hearts are less common in male/female friendships than women's friendships, and DH seems to have almost zero with his male friends. They wouldn't volunteer any information and he wouldn't think to ask. They are really close but in different ways. Banter prevails, and there is definitely much more of that in my mixed friendships, which i treasure. I wouldn't be seeing less if them if asked to by a new partner, and anyone who wanted to exert control on my leisure time wouldn't last long, but there is no chance of infidelity, DH knows them too and comes along sometimes and doesn't see them, or anyone, a threat. Get to know this friend, join in and rather than feeling threatened, consider whether this relationship is giving you what you want and need.