Best Friend's Mom

I moved in a couple months ago with my friend from high school and his mom because I started a new job and they lived in the area. His dad passed away many years ago so it's just the two of them.
My friend alternated between night shift and day shift, so he worked days for some weeks and then nights for others. This gave me and his mom alot of alone time. We spoke alot and sometimes flirted, just for fun. She's not the serious mom type because she's only in her early 40's, she had him when she was around 16 years old.
Last Friday night my friend was working and that same night his mom and I watched a movie and started cuddling. Things were about to go further but I stopped it and said I needed to sleep because I felt that it would be wrong.
When I woke up in the morning, I passed my friends room and saw that he was already at home and asleep so I went downstairs. His mom was making breakfast in the kitchen and when I walked in she ignored me completely. I tried speaking to her but nothing.
Eventually I went to the lounge and sat down on the sofa. She came in after a while and asked me why I left her that night. She said she felt so hurt that she went to her room and cried. I felt really bad for that so I pulled her on top of me as I'm sitting down and I start kissing her. Honestly, I never thought it would be so good. I thought that she would stop me but she didn't. We did this for a little longer and then she did something which left me speechless. She stopped kissing me for a bit and quickly took off her shirt. She then stopped and stared at me and I stared back in complete shock. She had no bra under her pj shirt. She was just there... completely topless, naked boobies and everything. I literally couldn't think straight. She had to take my hand and put it on her boob. After a few seconds, I came back to reality and started kissing her again and playing with her boobs. This all got cut short as a few moments later we heard my friend coming down the stairs. She ran and put her shirt on and we acted like nothing happened. We all three then had breakfast together.
We did not speak about what happened that morning to this day, almost a week later. I don't know how to bring it up. I just want to make her feel like she never felt before. I can actually see us doing the whole relationship thing.
I really like her.