I’m very much a feminist. However, the idea that most previously all-male colleges are now co-ed because men like to be around women, and that their co-ed nature has nothing to do with feminism, is ahistorical. There was a huge movement in the 1960s through 1980s to make the most elite universities and colleges (both public and private) in the U.S. co-ed for issues of access and gender equality - those were the universities and colleges with the best reputations and the best inroads into top careers, and it is very true that feminist and women’s rights movements put pressure on these institutions to begin admitting women. It’s no accident that most of the universities began admitting women in the 1960s and 1970s, which coincides with the women’s rights movement.
It has very little, historically speaking, to do with the fact that men like to be around women. If that was the case, Columbia would’ve never went co-ed, because Barnard is right across the street; and Harvard would’ve never gone co-ed, because Radcliffe was basically co-located. (However, that might be true now - few young men would want to attend a men’s college with no access to women. In fact, Columbia held out so long partially because Barnard WAS right across the street.)
However, the flip is true of Deep Springs. They’re going co-ed not because of feminist pressure; the trustees and the students wanted the college to go co-ed for a variety of reasons - including financial ones. Some prospective donors have declined to work with the college because of their single-sex status, and apparently, they also have lost potential faculty over it. Your admissions pool is deeper and more competitive when you can appeal to 100% of the population as opposed to 50% of it.
Tulane used to have Tulane and Newcomb, but I don’t think that’s the environment you’re looking for - plus they dissolved them into one anyway. Yeshiva University has the all-male Yeshiva College and the all-women Stern College, and they are in two different locations (Yeshiva is in Washington Heights in uptown Manhattan, and Stern is in Murray Hill in downtown Manhattan). There are a lot of Jewish yeshivas that are all-male.
There are also coordinate college arrangements - like Hobart College in upstate New York. Hobart is a separate, independent college from William Smith College (the women’s counterpart), but they are coordinate colleges that have a partnership and I think offer cross-registration and social events together - so while it is technically all-male, I think the experience is not quite like going to Wabash, Hampden-Sydney or even Morehouse (which is very distinct from Spelman, even though we do have some cross-registration and a lot of social overlap). Somebody also mentioned St. John’s University of Minnesota - which is a coordinate college with the College of St. Benedict. However, these two are also separate schools nominally but share a single academic program, and men and women take classes together. Again, it’s not quite like going to a traditional men’s college.
And some military colleges are still predominantly male - The Citadel, a military college in South Carolina, is 92% male, and the Virginia Military Institute is 89% male. If you are interested in STEM majors, many science/tech colleges are primarily male - Colorado School of Mines is 73% male, and the South Dakota School of Mines and Technology is 77% male.