Some of these questions such as whether to stay with your boyfriend or whether to have kids are questions you will need to answer yourself. The best advice I can offer is not to make any major changes- marriage, kids, breaking up, etc. until you're certain of what you want. Even if your boyfriend proposes before you've decided, it's always fine to say, "I'm not sure I'm ready. I need more time to think it over."
I went from expecting kids, to being unsure about the issue, to making a decision that I know was the right for me, so I can give you some pointers on how to make the decision. The first thing I'd suggest is talking to both people who are parents and to older people who decided not to have kids about their decisions. See what each side has to say. What they like or don't like about their decision. That really helps to clarify things. The other recommendation of what helped me is coming to terms with the fact that you can't know what it's like to be a parent without being a parent. All you can really know is what it's like not to be a parent. So you have to make the decision based on that. Are you happy and content without kids or is something missing from your life?
Extrapolating from the kid issue to the decision as to whether to stay with your boyfriend, I think the same thing applies. You can't know what your life would be like if you were single. All you can know is what it's like to share it with him. So you need to ask yourself, do you like sharing your life with him? Do you like having him to come home to? There's always going to be good things and bad things in every relationship, but just thinking of the total over-all picture, do you like what you see? Is it something you want for to always keep or not?
The issue of whether to stay with your boyfriend and whether to have kids may also conflict with each other. If you stay with him and find that you differ with each other about wanting kids, then another problem comes up. In that case, the next question you need to ask yourself is which is more important to you- the relationship situation or the kid issue? One of those might end up making the decision for the other. It's best if you can figure these things out before you get engaged. You don't need to make a decision over night, but it's good to give these things some thought.
About raising your attraction, I think it's normal for a lot of women's libidos to decrease after they've been in a relationship for more than two years, so that could be the issue with you. You probably know better than anyone what sort of things turn you on. If you're into thinking about different scenarios, you might want to try role-playing out some things in the bedroom. Looking at sex stories, may help get you in the mood or give you ideas for role playing as well. The website literotica.com/stories has a fair amount of different ones, although I should probably warn you that a number of the categories of stories they have may be disturbing to some people.
“This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn't the small green pieces of paper that were unhappy.” ― Douglas Adams, The Hitchhiker's Guide to the Galaxy