I completely agree. The dates are to close together and just because you use a condom does not mean it will work.
You will never know until the baby is born and you get a paternity test. There's really no way of telling since you had sex with both around the same times. Just because the doc said that was your conception date doesn't mean it actually was. And if you had a condom then the chances of it being your boyfriends baby is a bit higher. BUT it could still go either way.
I agree, DNA test. It makes no difference if it was unprotected or protected, NO form of protection is 100%. Does your partner know he might not be the father as well, and that you were with this person? If not, it might be time you start talking to him about it.
THe only way to know for sure is to have a DNA test done after the baby is born. Most likely it is the bf's but it's not a sure thing to say considering it was just a day apart from each other. According to a conception calculator your probable conception dates are:
March 25-April 2