D.D.
I understand how overwhelming it is to try to work and raise children and still live a "normal"life. I have 3 children 6, 7, and 8 who are very needy, I also work 45 hours a week on a demanding (24hour on-call) job. My husband at times catches the short end of the stick. What we do to prevent the drought in our marriage is plan dates. We schedule time for us to get away and enjoy one another. We also plan family time to ensure the kids get the attention they need from both of us.
I had to change my outlook on life to get here. I had to make my family my first priority and recognize that my career is ultimately a means to an end.
As for your husband turning forty - my husband went through some sort of mid-life crisis when he turned forty. I think it had a lot to do with the fact that he realized there were alot of things that he could do at 20 that he can't do at 40 and it was killing him on the inside. It passed over time but a little support from me went a long way.
I said all of that to say that you make the priorities in your life. If you really love your husband and want your marriage to last you have to put him first (well, second after God). You'll find that as soon as your priorities and attitude change about what's really important, your marriage will take a turn for the better. As for being spread to thin - do what you can do and let the rest wait until you can get to it! Life is too short for you to be stressed all of the time!!
Good luck and God bless!!