I'm tired of being nice

Just to start out I want to say that under near all circumstances I rather enjoy doing nice things for people. Friends, family, coworkers, and even strangers. I believe that there is inherent value in being kind for the sake of being kind. With that being said... My family relocated for my husband's job. He has friends out here and I had neither friends nor other family here when we moved. My husband is really close with his best friend, who lives with his significant other and their kids very nearby. In fact, the proximity is why we live in the neighborhood we do. I don't mind the closeness, our kids play with their kids, play sports with their kids, are close with their kids, and in theory it would be an ideal situation. However, I feel like I am being quite clearly taken advantage of. Whenever his friends, the ones who live close by and other couples who we are friends with, need a sitter, I don't usually have a problem lending a hand. What I do have a problem with is a.) when the "friends" who I am babysitting for stay out far past the time I was told, b.) when something comes up for our "friends" I will be asked to watch the child they are babysitting (whose parents are also "friends") so all these "friends" can hang out together, c.) when I am asked to babysit while my husband is invited to go out with all these "friends", and d.) when I cannot rely on these "friends" to watch our kids with any kind of reliability (something usually comes up, or I won't ever be given an answer until it's too late). As it is, I work mornings and drive the "carpool" weekdays for the "friends" who live nearby in the morning. I say "carpool" because it isn't technically a carpool when one person does all the driving. I reluctantly come home from work shortly before I have to pick up our kids from the bus stop, and then have our kids to watch while my husband sleeps. This means that I am already solely responsible for making sure our kids do their homework. For the most part I am the only one who actively makes a proactive effort to clean, aside from the two oldest girls splitting dishes through the week. I have a lot on my plate. While I find that there is always lots to get done, I make sure I make time to do things with our kids. Since my husband works overnights, it falls on me to get the kids up in the morning, fed, dressed, drive the "carpool", before going to work. During this time my husband could be/is sleeping. He then sleeps again after the kids get home. He usually wakes up for dinner and a few tv shows and then is off to bed again. I mention my husband and my schedules relevant to tonight's events. He was asked if I could babysit yesterday or the day before so our "friends" could all get together and go out. One set of "friends" left their kids in the care of the oldest sibling. The other set brought their child to me. Not in or of itself upsetting. What was upsetting is that although I was asked to babysit, my husband was invited to go out with them all. Though I am the one who does all the babysitting and carpooling in our house, he is the one invited out. Even though he had to go to work tonight after the outing, coincidentally missing out on all his usual sleep to do so, he was invited out. I have tomorrow off, but I was asked to babysit. While this was pretty frustrating, it was only further exacerbated by the fact that my husband seemed to not understand the gravity of how the situation feels for me. His response is little more than, "You could have just said no." Sure, I could have... but that doesn't change that he was invited out and I was not. When he returned he started to tell me about their gathering. I had to stop him. I let him know that it was probably not a good idea to talk about what they all did to the person who was left out of the plans to be a babysitter. To this I am replied to by being told it isn't fair that he should have to feel guilty about going. Now, he did ask me if I wanted him to stay. However, I was not going to ask him to stay. If he wanted to stay because it was what he actually wanted, he wouldn't have asked me. If he was going to stay it should have been because his friends were leaving me out to be the doormat, again, and that the behavior was not okay. If he stayed home it should have been because he wanted to stand up for me. It shouldn't have been because I wanted him. The only reason I'd have wanted him to stay would be because he wanted to do right by me. I am just at the end of my rope in this situation. It is clear that I am not valued or appreciated. While I am told by some of these "friends" that I'm too good for my husband, I was still left out. It is obvious that I might just be too good for this whole situation. My good nature and desire to be kind is my Achilles' heel and I am just sick of it being exploited. My birthday is coming up and all of these "friends" were already invited. I already hope they all bail out on it. What might be a good way to handle these "friends" and my husband's lack of understanding without straining the friendships of the kids?