I'm so sorry you are in this painful situation, and with 3 young kids in the mix, as well.
I am not sure what country you're in, but it's still difficult in most places, and in some place outright illegal, on pain of death, to practice homosexuality. Let's assume you're in the Western world, where being gay isn't a crime. It still common in more conservative areas, usually rural areas away from the coast, to be in denial of one's same-sex attraction. Your wife may have thought she needed to leave the woman-love stuff behind, settle down in a het marriage and have those kids. Now she's a bit older and realizing she has gone against her true nature.
Of course, it's not necessary for her or you to be monogamous with new partners, or to be single/unmarried to practice polyamory. And it's not "easier" for a woman to find a committed relationship than it is for a man. Women can find a guy for a one night stand quite easily. Finding a real committed relationship, with any gender, is pretty darn difficult. Maybe wife has found the woman of her dreams, maybe not. It's early days yet. She might want to just keep dating this new person for a year or two before making any major changes and upsetting the kids' lives and security.
In the past, it was not uncommon for a gay man to marry a gay woman, so they could present as cis/het to society at large, and carry on gay relationships on the down-low. In this case, you could certainly continue on as friends, even platonic roommates, while having romantic/sexual relationships with other partners. Older women who are not interested in having (more) kids can be quite happy poly-dating guys with kids, and even with a wife, as long as the guy has the free time. I am one of those women who has done this and has had it work out rather well. Any parent who is trying to date will have to put their kids first, of course. I hope your wife is, while she is all in NRE with her new gf!