Get over it? What's to get over? He had a life before you just like you had a life before him. You can either accept and be open to his child or you decide it isn't something you are comfortable with and go your separate ways. Either way it is a choice only you can make.
There really shouldn't be anything to get over. If you love your bf then you should love his son. The son is just more of his dad. Maybe you should look at if you are really worthy to be involved in his son's life.
I think you will get over the fact that your boyfriend has a seven year old son if you really love him. The fact is that he is with you now and he was honest enough to tell you about this as a matter of openness.