Re: Feeling angry because my wife refuses me too often
I don't think you're being selfish. I think part of the problem is the schedule. You're on a daytime schedule, she's on a nighttime schedule, and when you combine that with young children, it does make it difficult to find time to be intimate. You don't say what time she has to leave to get to work, but I would say by 3, she's probably legitimate in saying that she has to get ready for work. I would try initiating right after the kids go down for their nap.
As odd as it may sound, scheduling sex might be something worth trying as well. No, it's not as much fun as spontaneous sex, but when you have kids, ya do what ya gotta do. If it's scheduled that you'll have sex, say, every Monday and Thursday, in the afternoon, that allows both of you to be prepared. You can make sure the kids are napping soundly, she can get a little extra sleep or whatever, and you both know it's gonna happen.
Her "get it over with" attitude is another story. In all honesty, I used to be like that when I was with my ex. For me, it was a combo of low sex drive and no attraction to him (because he was a cheater). After having kids, sometimes our sex drives change drastically, and since you say she wasn't like this before marriage, I'm inclined to think that after kids, her sex drive has gone down. For me, mine came back naturally over time, although not until I met my boyfriend. For some women, they do have to see a dr and occasionally take some sort of med to help get back to normal.
You need to tell her it hurts you when she says things like get it over with or to find someone else. You need to explain to her that you love her, you want her, and you don't want anyone else, you just want to feel like she loves/wants you as much as you love/want her.
One last thing...although I don't think you're being selfish, how often are you trying for sex? If it's everyday, you might want to back off. She might feel as though you expect it every single day, and that's too much for her. Try every couple of days, or a couple of times a week, and see if that changes her response to you at all.