Am i doing the right thing for my son?

i had my son in september last year, his biological father got in contact when he was 3 weeks old, saw him 3 times then didnt bother coming anymore as he felt awkward being at our house bareing in mind i had just had a baby and had been in and out of hospital coz i had a blood clot on my lungs, he has just decided to get back in contact and i have agreed to meet up with him tomorrow, the one problem is i have been with my partner for just under a year now and my little boy calls him dada! what do i do??? i am so stressed about meeting him tomorrow as he was violent and abusive to me in our relationship, anone got any advic on what to say and what not to say to him??? please any help would be gratefully recieved! :)