Should I give my daughter his last name?

Devon
So I've known my boyfriend for almost 4 years. We have been together on and off (I was too young when we first met so we waited until I was 18, I am 19 now and we have been together for 4 months) throughout that period. I am currently pregnant with another man's daughter. He is totally okay with this, willing to raise her as his own. I've taken his son into my life as my own also, he has started to call me mama (he is 15 months). I don't know if I should give my daughter his last name or not. The father is not in the picture never will be, not even for child support. He has decided to sign his rights off, which I am totally fine with. But should I give her my boyfriends last name? I do plan on marrying him and he made is very clear he has the same intentions.