how do I deal with a vertical split in my thumbnail?

[MaMaLa321]

I seem to have managed to stop nail biting recently, which is amazing, but one thumbnail has a vertical crack in the centre. I am applying nail strengthener to keep it together, but is there any way of stopping it from happening in the long term?

I had a similar split in another nail. It has taken a long time to grow out but I kept the nail really short to minimise it catching and splitting more, and really tried to take care of the area at the base of the nail - rubbed in good hand cream, very frequently. The nail is still weaker there but it no longer grows through already split, and is much more robust than it was.