(THIS IS LONG BUT PLZ READ😭)

Okay ladies so I need the best advice you can give me. I've been with my so for over 3 years now and I've been living with him and his parents a little less than 3 years.

Backstory: so my bf's parents have been going downhill because my bf's mom wants to divorce his dad but his dad is still madly in love with her. The dad fought cancer for the longest time and finally was able to get rid of it (cancer in his neck) but SADLYY it came back a couple months ago and spread into his lungs. We all think he doesn't have much time to live because of how rapidly it is spreading now.

So my problem is his mom... I love her to death and she has been here for me through the toughest times (even more than my own parents). About 6 months ago she started telling me she's seeing this guy.. keep in mind this guy has actually came over to her house and met all her kids AND husband. I'm pretty sure they worked together at some point so that's why he came over. Well she's constantly telling me that she's going to leave her husband for him and move in with him. She always talks about how much money he has and all that.

My boyfriend has been really upset about the fact that his dad is basically dying and on top of that his parents are divorcing. He has cried about this constantly and tells me that he feels so sad for his 6 year old brother who isn't going to see his parents together like he did. I feel seriously SO GUILTY FOR KNOWING. I know it's none of my business to say anything (and I definitely WONT) but I'm afraid if my bf finds out I knew he'll seriously break up with me.

Just last night my bf was wondering where his mom was and freaking out because he thought something was wrong (she works late hours but didn't come home until 4 in the morning) but in reality I already knew she was going to see this guy.

His mom is like my best friend. We tell each other everything. I don't get mad when she tells me these things because of coarse she has nobody else to tell... but I feel like I'm completely in the middle of this and can't get out now. Her husband and my bf always wonder where she is and I just sit there quiet. Idk it just really bugs me that she would do this to her husband.. he's always listening to depressing music and he always brings her home things and actually makes an effort to be with her but she tells him there's no point to. She's a very independent woman. I know that she has fallen out of love and she needs to do what makes her happy but I don't agree with the fact that she's bringing down people around her. His parents have been together for like 15 years now so I know it's normal to want something else.

What do I do?

I just need a way to feel less guilty about this... it's to the point where I'm balling my eyes out when my bf does because they both don't deserve any of this. I'm just really afraid that this is going to blow all up in my face one day.. especially when she decides to actually move out. I would love all the opinions and suggestions I could get.