I spaced my children 3 and almost 1/2 years apart. I have to be honest, even at 4 an 1 It's very crazy in my house. I can't imagine having a toddler and a baby. I'd tell boyfriend to wait at least another 2 years. You'll be very very suprised how fast that time goes and then at least the first one will have a good sense of mom and dad and be out of diapers by the time the second one comes. Elliot was almost done Potty Training when Piper was born and 1 in diapers and 1 in pullups was hard enough for me. I also think each child needs at least 3 years of establishing themselves in the family before you throw another into the mix.
If you're afraid of them not being close, Elliot and Piper are the best of friends.