This is a really difficult situation. I feel for you.
Others have said some useful stuff about your partner.
I'm just going to offer something about how to really bat back the bullying situation to the school. This is orginally where the situation has arisen, and they should be doing more to prevent it.
I have dealt with this more than once, with different schools, both when I was married (now ex husband only had criticism of me to offer one reason why he is now an ex)
dealing with it again as single parent family later on, was difficult in a different way, and quite a lonely business, had to dig deep to find the strength.
It helped that I had experience of being a parent governor of a primary school and understood a bit more about best practice and how things should be dealt with, but secondary school was really not adhering to best practice i..e zero tolerance of bullying and in the end as a result partly of my complaints to the school, the head resigned.
As a parent, I listened to my child and tried in the first instance to strenghten their ability to stand up for themselves, and report bullying they were experiencing to a member of staff. Also peer support was important from friends in their peer group.
Advice I was given by independent organisations was never, ever complain about bullying verbally. Always do it in writing to the school. And keep your records of it.
Ask to see the school's anti bullying policy - which means that you can inform yourself as to what it is they should be doing. Some schools don't yet have one, or take the attitude that 'it doesn't happen in our school'. Which is ridiculous as it happens everywhere whether people see it or not.
And in our case the teachers didn't see it, and it went on for months.
In short, and sorry for the masculin metaphor, but when I dealt with hte last spate of bullying I had to literally 'grow some balls' as a mum. Speaking to the school in a meeting ranks as one of the most terrifying things i have ever done.
If you have a meeting, make sure it is minuted correctly as you will probably be very emotional about it and may not remember every detail afterwards.
Sounds obvious, but watch your language in said meeting as they can hold it against you..
Good to do such a meeting with a supportive partner (sounds like yours isn't being right now) but do it anyway.
And do it without delay. I don't mean to scare you but there was in previous years incidennt of suicide of a student due to bullying. So it can literally be life threatening for kids.
Insist that immediate action is taken and insist on a meeting ASAP.
Also needs to go in the minutes of such a meeting when the action will be reviewed (to make sure the problem is resolved).
Insist that the perpetrator is moved away from your child physically and that child receives emotional support. (emotional support for the perp is not our business and up to the school).
And then try to focus on the positive difficult in covid. And your child's strengths.
Wish you well. As others have said, doesn't sound like your partner is supportive so you are probably better off without one. As difficult as it is dealing with such issues as a single parent , I've grown into it and feel more confident about my ability to do so now.
If you need to talk to someone about it try Family Lives. Look on website. Used to be called Parentline. Just to add on Woman's hour this morning chief inspector of schools said some insightful things about how schools and parents should and can approach such really difficult issues.