Help..

Don't judge. I get enough from my family.  I'm 21 my boyfriend of 10 months is 34. I'm the happiest I've ever been. He's divorced with a daughter who I love so much!! The baby's mom doesn't like me although I have only met her twice but I can somewhat understand because they have only been divorced a year but separated a while before that. Anyway, I may be pregnant with his baby. I'm extremely happy about it. I'm not sure how I should tell him or what his reaction will be... Any advice on how to tell him I may be or should I wait until I know for sure??? Help!