I love my Muslim ex-boyfriend still

You are not culturally compatible and the U.K. will never recognise your marriage even if you wanted (and rightfully so). Moreover, I doubt that he would ever actually marry you at all given that he’s already downgraded you and you’ve accepted that (you’ve already signalled that you’ll give him what he wants at a cost lower than marriage).
Like most young women today, you have incredibly bad judgement in men and have selected somebody who will never yield the emotional payoff you desire.
While being willing to submit to his wishes is no bad thing, in this case you’ve crossed the line to doormat.
If you have any self respect at all then you need to send a simple end text with three words, ‘it is over’ and then immediately delete all communication mediums with him rather than just block.
You need to move on immediately and control your emotions. You then need to be aware of just how poor your judgement in men is when dating and avoid such cultural incompatibility in the future.

Before I start, I know what I’m doing is wrong, but please don’t shame me.
Me and this Muslim guy (I am Christian) started dating in July, we fell in love and he took my virginity (I wanted to wait till marriage but I loved him so much), he promised we’d get married, have cute babies etc. Initially he told me he wanted four wives but digressed and said he wouldn’t if I wasn’t okay with it. The whole month of July went so well, we had one argument where the four wives were brought up again, and I got upset, but I then agreed, because at that point I had fallen so in love with him that I would compromise just so that I could be with him. I can’t imagine a life without him. The next 2 weeks went by perfectly fine, but then he broke up with me in the middle of August. At the time, I was so confused, he said he was confused with himself, that he thought he was ready for a relationship but wasn’t. I cried so much that day. He told me to take 2-3 weeks for myself to come to terms with it and that we can stay friends. I agreed because I just couldn’t let him go.
The first week was okay, but then it just hit, and I would cry and tear up almost every single day. I waited out the whole 3 weeks. We talked on the phone on that 3 week mark, he asked how I’d been etc. And I lied that I was okay and that I was over it. Later that day, he asked if we could “f*ck as friends” but I had to promise to not catch feelings or expect a relationship out of it. It broke me a little but I agreed because at least I could still have him. We met in person on the 4th week and it’s like I fell even harder, I was still so in love with him. But I couldn’t tell him, even now.
Time has gone by and we’re still friends, we talked on the phone all day yesterday, and we happened to talk about our break up. I told him July was the best month of my year, and I asked him why he broke up with me, he told me “it wouldn’t work out” because I didn’t want him to have four wives. I told him that it wasn’t the case, that I loved him before enough to allow him to have four wives. But I didn’t confess anything to him. He asked me if I wanted to be part of that and I said yes. He told me yesterday that recently he’s agreed to let his mum pick his first wife due to stuff at home. And if we were to get married I’d be his second wife or whatnot in 3-4 years time, I’m 21. And I love him so much that I’m willing to wait all that time to be with him. I sound crazy, but I can’t imagine a life without him. Even though he’s using me for sex until he gets married, then I won’t be able to touch him anymore, and it hurts. I really want to be with him, and I really wanted to be his first wife at least like he initially wanted. I don’t know what to do. I feel like I’ve lost all purpose in my life, I’m not happy without him, and I just want to be with him.

you're right she needs to end it, but she asked not to be shamed. how's that going?

Why would I make this up? How could I possibly make something like this up and entertain it. How else am I to show you that what I’m going through is real. I wish we can switch minds for a day to actually feel what I’m going through.

I wouldn’t say that acknowledging her flawed choices in this is shaming albeit I do think people would make better choices if they held themselves more accountable. The people of TSR are not her friends, we should give her objective advice rather than sugarcoat what she needs to hear.

I actually went softer than I normally would because being willing to be a wife and mother in her early twenties rather than engage in the actions of a lot of people nowadays is something to be applauded.