Thanks folks for all the feedback and advice. The heart connection and love are important to me in my sexuality, and I think having a secondary love relationship would fit me where I'm at better than more casual hooking up or swinging.
Having identified as bi at one point in my life, I agree that bi women would be a good fit for me and my situation compared with lesbians on a lot of levels. I don't expect that I'm going to go out and sleep around casually (not that there's anything wrong with that). I just want to desire and be desired again, and be able to act on that in the world, to connect with other women in that way. Monogamy was something I fell into with my wife, more by her choice than mine, and because for the first several years our sex life was so rich, I didn't miss having other partners. Besides, it was what was expected.
About my wife's loss of libido - she's still working on trying to get it back, but not particularly urgently from my perspective. She mostly thought it would resolve on it's own once she got through menopause, so we spent about 4 years just waiting, and then more recently she's gotten some medical help with it. She's correct in saying it's something she has to work on in her own way. She's gone to her doctor, who has done some helpful things, but mostly the information about loss of libido in menopause seems to be 'lots of women in menopause lose their desire; live with it'. I've asked several menopausal women I know, and 8 out of 10 of them said, yes they'd lost their libido mostly and it's a relief for them. They seem about as disinterested as my wife is in doing anything drastic to get it back. So I'm not feeling really hopeful.
About my use of the word 'asexual'. I understand that it's used to refer to someone who may maintain romantic and cuddling relationships with others but isn't interested in sex, which fits my wife. I get that it's a lifelong identity for some and if people think my use of the word to describe my wife is disrespectful to those who identify that way, I'll find another term.
I'm a decade younger, and my desire is still fine, and she went through early menopause, which exacerbated things. We've been trying this and that for about 5 years now, and I just can't respect myself and wait any longer. She has very bravely been honest with me about what she's up for and not up for. We still cuddle and kiss and have a lot of affection for one another, she's has been willing to have sex with me occasionally (every couple of months), and has an orgasm when we do, but it's a far cry from our former sexual connection. 'Willing to' is so vastly different from 'wants to' that it still makes me cry. Our current arrangement is that I will not initiate sex (it is just too painful for me to be turned down all the time, or to maintain that hopeful place) and if she wants to she will initiate. If she's only having sex to please me, we need not to be having sex. We haven't tried the sex therapist, but we've agreed that she's the lead on her own process and body, so she'll have to decide on that.
I've taken some steps to connect with the local polyamorous community in my city, and I'm thinking about which of my poly or poly friendly friends to talk to. I need to talk to my partner a bit and agree on what I will give as a reason for our shift, because friends will ask and I need to have something to say. My fear is that some will assume it's me wanting to cat around and her giving in, but it's a lot more complicated than that. I know coming out is a process, and definitely 'fuck what they think' is a good strategy. However, I have a conservative, private wife whose boundaries I need to respect too, so I'll have to feel my way on this one with some consultation with her.
Anyhow thanks for the feedback. I'm doing a bit better today. Weekends are hard, with a lot of time for all the layers of feeling to hit. I'm mostly focused right now on building some support for myself, as my wife can't be expected to be the sole place I bring my grief and sorting out to.