AIBU to go off sick?

[Somewhereabove]

Due to relationship breakdown my mental health has deteriorated. I’ve stayed at work throughout but I can’t concentrate, are missing things, easily distracted etc and I keep thinking about going off sick but I just have so much work to do and would feel guilty to my team who also are busy and would all have to pick up my workload. But on the other hand I know that I’m pretty useless at the minute and it’s just not getting better. I hate being off sick at the best of times, always feel so guilty.

Two reasons why not to. 1/ Would you not be better off at work keeping mentally and physically occupied and 2/ Many jobs are precarious at the least at the moment and i personally wouldn't want to risk my job hence adding to my problems.

Harsh as it sounds and I'm sorry for your break up, but sometimes you just have to soldier on

I agree with above.

Do you sleep well? What do you do to make yourself feel better?

You'd be better off squeezing as much time outdoor as you can (with work and at this time of year, I appreciate it's likely to be very little during the week)
and exercise.

If you think your state of mind is affecting your wellbeing and ability to do your job in terms of concentration and staying on top of things it wouldn't be unreasonable to have a discussion with your GP. I'm sorry you're in a bad place.