This will be long but I don't want to drip-feed.
DH and I have three young children, we both have busy jobs and moved a few years ago to a new city, so we have a limited support network, certainly no family locally. We bought a dump of a house and have completely renovated it. So, for context, we have had a hectic few years and have been through the stress mill.
DH has a history of depression, mostly untreated, though in the last year he has been receiving treatment (anti-ds, CBT and counselling) and is making big improvements. This has often manifested itself as him rejecting the company of others and isolating himself which has made me feel quite alone in it marriage and lonelier more widely - I do have friends at work and friends I have met locally but we rarely socialise as a couple.
A sticking point for a few years has been our sexual incompatibility - DH would happily have sex daily and I not so much, but a large part of this has been a lack of attraction to him. He can be quite short-tempered and dismissive of me, plus the usual grind of living with someone who has different standards of living to you. For context, he is an incredibly engaged parent and we are a serious team when it comes to the raising of our kids.
So, predictably, as his fitness and attitude has improved over the last little while, he has been going out more. There is a woman he works with who I have always known he has found attractive - neither of us are very jealous by nature and have been open about things like that in the past. A few months ago, he was suddenly going out more, making an effort to look nice and then told me one evening that he had met with this woman to clarify to her that nothing could happen. At around the same time, he suggested that we begin to have an open relationship in the interests of remaining together but for both of us to be happy. I clearly explained what he had done, why it was awful, why it really couldn't happen and he seemed to get that.
Fast forward to now and I notice similar behaviour changes - more of an effort. He has been exercising a lot, being nicer to me and I have found myself much more attracted to him, both mentally and physically. He raised the issue of an open relationship again. Feeling a bit alarmed by this change in his behaviour (he is very predictable by nature) I asked him if he had continued to see this woman. He admitted that he has kissed her once, whilst at work.
I feel in many minds about this. Neither of us have nurtured our relationship as we should have done and I know there are a lot of points at which I could have been more engaged/done more. I don't feel horrified at the prospect of an open marriage, but have no idea how this would work in principle and actually, feel he is asking permission to have an affair with one person specifically, with whom he clearly has a close emotional connection.
I worry that my lack of horror about this proposal means that things are over with us.
I suppose I just need some outside perspectives on this. There are not many people I can discuss this with in an unbiased way and because I don't yet know what I want to do moving forward, I want to limit my discussions.