Either stay with your wife and put some boundaries between you and temptress or throw away stability for the weed smoking homewrecker.
She's always a potential time bomb given chance because she decided OP is go. But she's probably manageable.
I wouldn't really go for a sit down over it, but some things to consider.
1. What makes you bangable for her is the emotional connection and prior tension, unfulfilled. But mostly emotional connection. If she wanted some random dude she would go on a dance floor in a bikini.
2. She wants you to stay around, and the intimacy you get with someone after you had sex (cultural thing); for her that's the only thing missing, which is why, in her mindset having sex with you is an easy decision, you don't have to stick around for more - having sex with someone committed is a strangely easy decision - everyone is afraid of commitment, but you're committed so when the other part accepts that they're not expecting you to priorize them and be boyfriend material. Of course, I'm not telling you to go for it (don't!).
3. Above all that, you're an escape from her life/reality. And she assumes (if you go for it) you also want/need that escape too. She wants to be herself, she probably doesn't feel that she is her own person or in control in her everyday life. She's basically being most of all a friend for you, even if she doesn't know how and it gets really mixed. If anything happens it's via consent (contrary to other people said I don't she's being manipulative), she wants to be there for you, but I don't think she's in love (apart from a slight crush) nor is she thinking long term. Smoking a joint and having sex is not long term, she's not taking you for dinner at a fancy place, nor are you. You probably lowered her expectations and she's ok with it.
As for what you should do, hell if I know. She seems like a sweet girl, you can insist on being just friends and brush aside her advances (I wouldn't talk about them, just ignore them, after a few of those she'll realize you're not interested). But you have to be in control. Of course, you're still playing with fire. Friendship is an interesting prospect though, but you have to draw lines of what you won't do. Like going up to her chambers (I like chambers better than "room"). I'd probably go with this from now on, you can get together for drinks, you can be together with other friends (almost preferable - you can be the guy that organizes it, invites her and invites other people too, to her surprise), but you don't want to be alone with her in a privacy setting. Also bear in mind that, switching places a lot like, coffee, dinner, some bar, someone's home, might be an afternoon that went into the night but for her that's 4 places she's been in, seems like an awful time and eases up people. If you want to close up on someone change a lot. If you want to have coffee with her, have coffee and then fuck off somewhere else. Don't encore, you'll just end in her chambers.