Husband (35) has a weird relationship with coworkers wife and my (32/f) ex friend

Ok where to start with this. My husband (35) is incredibly hard working, and has been able to achieve significant success in his career, through luck but also through busting his ass. As such he is in a position in his career that most men don’t achieve till they are in their 50’s. Financially we are very well off.
About a year ago we moved to a new city for a career opportunity for him, which we were both excited for, even though it meant leaving our friends and family behind, we did not know anybody in this new city. When we moved here we were introduced to one of my husbands colleagues, who is at a similar position in the company, we’ll call him Dave. Dave is very successful and smart but older (60ish) and honestly not very attractive. His wife Natasha (30) is young, and very beautiful, energetic, tho immature... this might sound callous but it’s obvious that their relationship is not necessarily based on love, more of convince. She doesn’t work, spends lots of time traveling and shopping, and Dave lets her pretty much do what she wants, as he works so much. They don’t have kids. Something to note too, Dave ended his first marriage, of 20+ years, leaving his wife for Natasha.
When we moved here Natasha brought me into her circle of friends- who she mostly attend church with. It wasn’t my crowd but it was very lonely moving to a new city without knowing anyone. Natasha and I began hanging out more, though I would never call us close though. She would often complain about Dave when we met, and issues with his health/behavior typical to that of a 60 y.o. When I talked about the stuff my husband and I would do- hiking, dancing, traveling, or going out together I could tell she got a bit jealous. I did not do this on purpose but she would ask what we did true past weekends, etc, etc. As two couples, we and our husbands together, would also spend time together, dinner, theater, etc.
A little while ago, Natasha and Dave, invited us to join them for a few days in Hawaii where they had rented a house. The place they rented was beautiful and huge, and they said that it was on them, which was more than generous. When we arrived, Dave spent most of the days sleeping, reading, etc. Where as Natasha, my husband and I would go hiking, go out, and do activities, this was decided before we started the trip as Dave likes to spend vacations relaxing while we are more active.
I felt a shift during Natasha at this time, as she clung on to my husband all the time. He is a good looking guy- and she would constantly compliment him, his body, his muscles, all the time. She was also very physical with him, and take his arm when walking, hug him, etc. My husband would also pay for everything while we were out, meals, trinkets, drinks (he felt he should as they paid for the rental) which added to the weirdness of the situation, as it felt like he was her surrogate husband in some ways. One night the three of us were out dancing and Natasha started grinding up on him and laughing. They danced closely for a bit till I asked to cut in, I could tell Natasha was annoyed. I didn’t want to ruin the vacation so I said nothing, but felt hurt by her actions.
When I confronted my husband about her behavior he just said she was having a laugh, and it was harmless, and they were just friends.
When we got back from vacation, I consciously decided I would distance myself from her, not instigating hanging out together as much. It was hard, bc most of the women I had met were from my relationship with Natasha. About a month after we get back though my husband asks me if it’s okay if Natasha come round for dinner- what?! Apparently Natasha had been texting my husband since we got back. I looked through his phone and it’s innocent enough, mostly her complaining or asking advice or asking how he is but still weird esp since we haven’t talked as much. I confront my husband about this, and he says that they are friends as well. He also decides to tell me that after we got back Natasha dropped by the office to see her husband (who was conveniently in a meeting) and dropped in on my husband- they went for coffee, where she told him she was seriously depressed and valued his friendship. My husband told her that if she needed anything he was there for her.
Anyways Natasha comes over for dinner and it’s beyond awkward as she pretty much ignores me the whole time and is all over my husband- it’s like I’m watching two pple on a date. My husband tries to include me, but I’m also just beyond done and spend the night pretty quiet. When Natasha leaves she gives my husband a long hug and asks him about grabbing lunch that week at work- wtf?!
I am done with my friendship with her but my husband feels bad for her- esp since she confided in Him about her depression, and wants to keep the friendship, also since his relationship with Dave is important. He just thinks that I am being mean and thinks Natasha is just playful nothing more. I told him I thought it was weird about Natasha txting him and Him not telling me they met for coffee but he says that he felt bad disclosing what she told him.
I am not sure what to do- give my husband an ultimatum? Try and est a friendship with her again? So that she leaves my husband alone?
TLDR: Husband (35) has a weird relationship with ex friend


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