You are the same person dealing with the obsessed ex, right? This might complicate that situation further, if he sees that you got pregnant the obsessor will feel that his view of how things are "supposed to be" have been permanently violated and therefore he might see his life as "permanently broken". This type of reaction is something I can not predict. What a situation, this is well beyond my level for expertise that's for sure.
I suggest talking with your parents about your pregnancy. Parents are usually supportive, they have the experience of raising you and they will probably be willing to take a strong role with raising your baby. The fact that your current boyfriend is supportive is a good thing. Often times in situations like yours, a boyfriend tends to abandon his female partner to avoid dealing with the responsibility. Now that you are pregnant you need to make sure you stay together, you will need support from him as much as he needs support from you. Make sure your feelings for each other stay strong and that you both know that you want to be with each other for the rest of your lives. Your relationship is now entered an irreversible biological bond.
At a last resort, if you feel you and your BF would be unable to raise the child by any means, your state should have a "safe haven" law meant to deal with exactly your type of situation, where the government would then take charge of the care for the newborn child.
Best wishes to you.