lb24 I have been married for 38 years and have never had any reason to doubt my wife, and that doesn't mean its all roses, there are days when I could gleefully strangle the cow, but if you are having problems this early then I would have to say this is not the right person for you.
When you have to start making excuses for their behaviour to yourself or anyone. Or if you have to lie to yourself about why you're with them. It's easy to say you love someone but to mean it and know it inside you is different.
I agree with Wendy. (Great answer by the way) We all have to accept the foibles and failings of our partners, but when you find you're constantly forgiving the same old 'crimes' and experiencing upset after upset, it really is time to accept, enough is enough!