Mimi - The male erection is a complicated physical event that can be affected by both physical and psychological factors. Although it may have something to do with the relationship between you and your husband there are lots of other factors that could be getting in the way. Getting a physical work up is always the first step. If the two of you have found your relationship strained for one reason or another try talking with him about the relationship in general and your sex life together, in particular, and whether there is the need for some outside intervention.
Unless you are applying something to yourself that is causing your husband to lose his erection, I doubt seriously that you are the cause. There are many things that can cause erectile dysfunction. Almost all men experience ED at some time in their life regardless of age. In fact, one of the resident experts here Healthgal, just wrote a sharepost called "40 over 40 is the new ED awareness slogan." In the article, Healthgal writes: "a new survey reveals that most guys who hit the age of 40 are unaware that ED may come knocking at their door. The reality is that 40% of men over age 40 experience some ED." You can read the entire article here.
If you and your husband feel it is a concern, the best thing to do is to see your doctor. While online sites like HealthCentral.com are great resources for information they can not take the place of your doctor's sound medical advice. The best thing is to research all the information available and use it to ask all the right questions so that you and your doctor manage your care to the best of your abilities.
Here are some links to help you understand what could be happening, and give you the information that will help you when (or if) it's time to see the doctor.
Here is some information that might give you some ideas on how to approach this. You can read about erectile dysfunction here, the basics and what some of the causes are. The symptoms are listed here. There is a good section about coping here that might have some information you find helpful. Should your husband be diagnosed with ED, you can read about drugs commonly prescribed and treatments here.
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Anyway, feel free to ask any questions you have and I hope you will stay in touch and let us know how you and your husband are doing!Vicki M