I'm sorry you're feeling so isolated... I empathize completely with you.
Have you thought about joining a playgroup with/for your kids? That is a good way to meet other moms/new friends. Our congregation (unitarian universalist-all faiths, ethnicities, etc. are welcome) has an outreach to parents of infants and toddlers, where they open the toddler room and a moderator brings snacks, juice, coffee, and the parents can let the kids play with extra supevision so they can have a bit of a break. If you don't want to go through a church/synagogue to find a playgroup, try googling your area and the word "playgroup" or checking Meetup.com for playgroups.
Have you thought about joining a class, like yoga or pilates or taking swim lessons or craft lessons of some kind? That is a good way to meet new people and be "doing something" other than being at home. I find that when I'm active (as in, not feeling "trapped in the house") with my son, I feel less lonely.
Another thought along these lines: how about volunteering with a soup kitchen, or a women's shelter, or some other good cause that inspires you---doing good for others, and feeling part of a group making a difference, is a huge way to lift your spirit.
You might also try asking your husband's friends for connections on playgroups or other activities you're interested in-- this might help you develop a stronger connection to them, and by reaching out would let them know that you're interested in more of a "friend" relationship, instead of a more "acquaintance" relationship. If there are other moms in your husband's friendship circle, why not take the role of organizer, and suggest to one or more of them (depending on what your comfort level is) to take the kids to the zoo, or have a picnic or invite them over for a craft with the kids or a barbecue or whatever.
Best of luck, hang in there, and keep reaching out and someone will eventually reach back!