Where do I go from here?

I've been with my other half for 5-months I have a child who's 3 at the moment my other half is in a predicament my other half has got someone pregnant and had she baby in December that girl is his ex they have history because they were together for 5 years

He started reaching out and being horrible even though she’s in a relationship with another guy they keep harassing my other half and myself this girl cheated and all sorts she stayed with the guy she cheated on my other half with she also did other things during her pregnancy she took drugs and alcohol she posted out over social media I don’t know how to give my opinion on this type of situation because she called us up on Monday asking my other half to meet her and myself it wasn’t because she doesn’t know who the father is or anything like ( what I gathered from the conversation was because she wanted to show off her child like a trophy basically) that is because might be she is lonely because she was dumped and she’s jealous. in October she messaged me and started having a go at me once again she wanted to talk to my other half but he didn’t want to talk to her she also stalked his family to get his phone number I know they have history but one thing that hurts me is that he wants to start a family with me I have no idea how to react I dont want to be selfish is stressing because I already have a three year old he’s the sweetest person on Earth and I don’t want to see him hurt from what I’ve heard from what I’ve experienced she’s exactly like my son’s father very abusive very controlling and manipulative… his family loves me and support me and and his family really like me and they don’t want my other half to lose me over the situation but I don’t know how to cope without looking selfish or looking like I don’t care this is really upsetting I’m a mum I know how to look after kids but I don’t want to be involved with toxic stuff because I dealt with a lot when I was with my son’s dad I cannot deal with people who are toxic on violin or abusive it does not bring me happy memories I just want to let it go and just forget about it but it’s not my choice but I really just had enough of being harassed and being called names and stalked that girl literally makes fake accounts to get to him it really hurts me because the love of my life I’ve never felt this much love in my life and appreciation and everything else is literally the nicest gentleman anyone can meet I don’t want him to go through what I had to go through they say you have to learn from your own mistakes at the end of the day this could hurt him for good or he could never be happy ever again