Cutting out FWB

I (M27) have been FWB with a girl (F26) for 3 or 4 years now. And it wasn't constant sex it was just kind of a really good friendship of supporting but constanly falling into sex scheme. We have both agreed multiple times to stop and just focus on others. I tried multiple times and even wanted to break of friendship for us both to fully focus on ourselves, especially since I have been dealing with some depression in past years and have been having episodes of going full on despair. She always convinced me thats stupid and lets just be friends. I was always feeling bad of cutting somebody out because I felt like an asshole so we stayed friends.

So recently I started dating via Tinder and Facebook Meetings (not sure what its called in english). And haven't had any luck. I was out with FWB and we went to her place to watch a movie. We both were feeling it a bit and things started to be a little touchy. I noticed on my phone I got a notification that a girl liked me on Facebook Meetings. But then I just kind of ignored it because I have very low expectations. Tht night we had sex and agreed to not do it anymore, but I know how that talk goes. Then I spent 2 days thinking about it and decided I want to matvh with this girl om facebook and see whats up. I realized after that that I have doubts about doing the honest right thing. So I told my FWB how I'm feeling and she said I'm being stupid and that she supports my decision in dating. When I told her I am talking to this girl on facebook, that day she started being a bit horny and dropping hints. I asked her mutliple times why is she doing this now because I am talking to this girl. We hung out once more but strictly platonic. But these hints from her are still visible.

Fast forward to today, I have a date with girl from facebook soon and realized I will have to explain my previous relationships at some point. And I would really love to be fully honest and respect her feelings and decisions. So I thought, I can't hang with FWB, this is such a burden to bear. I don't know how to explain I had sex with her and I am still seeing her and she knows I'm dating. I told my FWB we should see each other less, because I am anxious about it. Especially since she was dropping hints she wants sex again I don't know what to think of that anymore. She started insulting me and was clearly mad.

I have never been in a relationship and I don't know what is right. And I got myself into this shit. Should I apologize to my ex FWB. How should I tell this new girl this if it comes to second/third date?