Divorce help uk please 🤞😬🤞

So me and my OH are engaged but he’s still married to his ex they split up 7 years ago and I don’t actually feel right being engaged to him while he’s married even tho they aren’t together is this normal or am I being stupid 🤷‍♀️ anyway I’ve stopped wearing my engagement ring and told him I can’t wear it to work I’ve tried to talk to him about it before but he just seems to get frustrated with me about it cause he can’t afford to pay for the divorce he never sees anything from my point of view seems to be his way or no way 😩 anyway is a Legit way to get divorced that’s not over the top expensive I’ve seen a lot of online ones but worry they are scams or there not finalised or something 😖 please help thank you 😊