How do I talk to my dad...?

So my dad lives with this lady and shes really nice, I've known her all of my life but not like super close or anything, my parents were just friends with her and would say hi all the time and catch up but not the type of friends that would come over all the time you know.. Anyways, they're living together now, it started out as room mates but then they started to date and be all in a relationship and such.. Whatever thats cool I liked them as room mates too but a step mom is cool too right.,. Anyways, shes kinda uhmm ****** ahaha from drugs and stuff and I mean I can relate ;) But I really like talking to her and hanging out with her and my dad is way more relaxed and chill and stuff around her and I really really like it.. They've been arguing a bit about bills and whatever and he keeps saying he wants to leave and such but then they kiss and make up rightt. How do I tell my dad that I like her alot and that I like him around her and stuff.... I have a hard time communicating with him as it is soo this seems tuff.. How do I tell him that I want her to be my step mom and I want them to get married and whatever and that I'm happy they're together ?