I would vote for not forgiving him and spend some time apart and see what you really feel about this whole thing. In the main time, establish your bonds with friends and see the bigger world.
You two should be still in the phase of great passion and commitment and his behavior showed you that he didn't really care about your feelings that much, or he is too self-absorbed to be any good for you.
During a long term marriage there will be many difficult periods and you will be going through a lot together. Please do yourself a favor and think in 10 or 20 years, if the love and passion between you two right now could serve as a fountain you can draw your love and strength from when things get tough. I think if you are not 100% sure about spending your whole life with this guy, don't rush into marriage at all.
It's probably hard to leave him at this time, but trust me, it would be much harder when he does this again and you two already have two young children...
