I want to fuck my girlfriends mother

So I met my girl on a dating site. We've been together for 2 years and now have a beautiful daughter. I met her mother when my girl was 5 months pregnant. She was curved in all the right places, long dark hair, smart, and funny. I feel in love that day. Months go by and it doesn't seem like much but just a mutual mother and granddaughters father relationship. But, up until now I see her checking out my bulge a lot. When I catch her staring at my penis she turns away and looks at the wall. I wear skinny jeans so you definitely can tell I'm packing. My girl doesn't want me to wear them nor sweat pants for this reason. When it's just me and her mother by our selves we look at each other in the eyes and the feeling is electric. I just want to rip her clothes off and fuck her. Then there's times when we look at each other and we look away real fast when I guess we notice we both are stirring into each other's eyes. Lately I've been trying to find ways to come over to her house( as she works from home) just to see what could happen. But almost every time somebody comes home( her mother) which is still alive god bless her soul. We had countless times being the basement as I would take water down there from helping with the groceries and she would follow behind. But as we are down there I panic and hurry back up the steps. Idk if she feels the same way as I do but I'm hoping so. Me and her daughter are together but it's a rocky road. I'm loosing interest but never told her. I'm not even interested in having sex with her anymore as her mother just got my sex drive focus. She hasn't been in a relationship for years and she hasn't had any guys or dates as well is what I was told by my girl. So I know that the booty needs to be dusted off and I want to do so. She wears tight leggings around me and that ass is so fat. I just want to grab it! She is curved and I love a woman with meat on them. The last time I tried to make a move I asked her if she could watch my daughter because I had some important meeting to go to. She said yes. I came back and was dragging it out to not leave yet so I started to feed my daughter. She was so close to me I started to grow in my pants. That day I didn't wear underwear because I wanted sex to happen. I seen her glance at my dick a couple times and she kept getting up from the chair and looking out the windows. Next thing you know i get cockblocked by her mother. Ahhh!!! I just want to sex her so bad. I know she wants the D. What should I do? Should I just make another power move and accidentally rub up against her by giving her the baby? Or just leave the lust alone