I lost my babies once nd my bf wants to try again, what should i do?

Okay, me nd my boyfriend have been talkin since October 16, 2010. Nd we have been official new years! Nd I had got pregnant and lost the baby(s), it was twns, he was super excited and he has been saying to me since about the 3rd month of us talking that he wanted to hve a baby with me and that he was in love with me bc I was so different from all the girls he ever been with. But he has girls from the past sill talkin to him nd idk if I should be worred bc everytime I ask him about it he tells me "u know I'm in love with u and u have my heart, these girls are low class" but I sometimes feel like he still talks to them. Hh wants to try again to have a baby with me but idk if I am ready to deal with it just yet. I am 19, nd going to school to be a nurse practitioner, so my future is bright. But there is a part of me that wants to have a baby now because I wish I wouldn't have lost my first nd I accepted him or her already. I am not worried about him not taking care of his child bc he has one child already nd he is a GREAT dad. Should I stay with him? Should I let him gt me pregnant? Please help me...