You'll be fine. If he knows you didn't tell him everything, he has thought about it and he cares. That is good. Trust me my friend, if he was going to leave you for her, he wouldn't be with you for as long as he has. In a sense, 6 months might not be considered long compared to other relationships, but it is long enough to fall in love, create intense feelings, and especially moving on from former relationships. Talk to him and open yourself up, him assuring you of his emotions are much more adequate than a stranger over the internet doing it. =]