How can I learn not to react when I'm upset?

Thank you for asking this important question.  It's clearly causing you distress. This is a common issue, and something that can certainly be improved. You are clearly aware that you lose control when you and your husband argue. And you want to work on this issue.

The next step is learning to know the warning signs (or triggers) that you are starting to lose control.  Knowing your warning signs and intervening while you're still in control can help make arguments more productive. Do you feel your blood pressure going up? Do you start feeling anger based on previous situations?  Do you start sweating? Or feel nervous or anxious?

Is it possible that you let your frustrations build up, then let them out all at once when a minor disagreement presents an opportunity to vent? This is a common style that people utilize with the goal of minimizing fighting. However, letting it all "pile up" until you "pop off" can lead to worse arguments with little positive impact. Arguing is normal and healthy.  In these situations, the argument doesn't result in growth or resolution.  

"Fair fighting" is key to having arguments that have positive, lasting results. There are online resources about fair fighting, or you can seek the help of a counselor.  If possible, couples counseling can help with this too. Part of fair fighting includes staying in control of emotions, staying on topic, and reaching a resolution.  

You may also want to reflect on any arguments you have had that actually helped to improve the situation. Can you identify the behaviors from these fights that actually seemed to help?

As far as doubting the relationship, that's hard to address without further information. I would need more background on your marriage to answer this.  What is your day-to-day relationship like?  How frequently do you argue?  Do you have more good times than bad?  How long have your been together? Is your husband truly the source of your anger, or is it other sources?  How happy are you with yourself regardless of your relationship status?

I applaud you for seeking help with this concern.