Tinkerchick, I understand how you feel. Being married to a medical student can be very trying. Others who have posted have offered great ideas for sustaining a healthy relationship, and I completely agree that love requires some big sacrifices. However, if you're concerned that the biggest sacrifice may be your relationship, I think that is a fair concern.
I may be reading too much into your posts (and conflating your anxieties with my own!), but it sounds like you are worried that your husband will be so committed to his studies and career that he puts you and your marriage on the back burner for the foreseeable future-- to the detriment of you, your marriage, and probably him. That, in my opinion, is a very legitimate and not necessarily selfish concern.
My husband is a medical student. At first he really tried to lead a well-balanced life, but it just wasn't possible for us. He wants and needs to study a lot. It is very difficult for me to get his attention. I work 60-80 hour weeks in a career that I love, but always make sure I'm home at a reasonable hour to cook dinner for him. Typically we get to talk for about 15 minutes each over dinner, then he goes back to studying while I clean, do laundry, pay bills, and finish whatever work I had to bring home. Weekends are not much better.
At the suggestion of others in our position, I've gotten involved in the community and started doing more with friends; however, I don't really want to be completely independent and happy on my own. I married my husband because we are awesome together. I don't think it is very healthy for him, or for me, or for our marriage for me to be out doing my own thing while he studies alone.
Hence, the tension at which I previously hinted. I am trying my best to be supportive-- so I certainly don't want to tell my husband he should study less, or consider taking a more moderate approach, or think about less time-intensive specialties. At the same time, I want to look out for him, and I don't want him to emerge from his studies in 10 years and realize he missed out on our family life and all things we believe in doing together.
You probably already have a good idea of what your life will look like in med school, and it may or may not resemble ours, but if these are the kinds of things that concern you, I encourage you to talk to your husband about your fears. I have to be very careful with my husband to make sure that he knows that I am not trying to undermine him with my worries, but talking really does help. Together hopefully you can start to find some agreement on what's good for your marriage-- not just for his dreams or for your needs.
Good luck.