Hi Bernewode, and welcome to the forum! Hope you find us all informative and entertaining!
The split in the oak chopping board is almost certainly down to using green wood, then taking it into a centrally-heated environment. All timbers have some moisture content, the amount depends on it's condition (freshly felled, air-dried, kiln-dried, indoors, outdoors, etc) and on the time of year (wood tends to absorb moisture and swell during the wetter months, lose moisture and shrink during the drier months).
The best way to ensure that a piece of work stays together is to use timber in a suitable condition. So, for a chopping board to be used in a nice, warm kitchen, a piece of well-seasoned dry wood conditioned to centrally-heated rooms would be the best starting point. You can do that in a number of ways - either buy your timber from a merchant kiln-dried to about 10% moisture content, or buy 'air-dried' wood (which will be somewhere between about 15% and 25% moisture content, depending on time of year and where stored) and leave it to settle for a few weeks indoors, whereupon it'll probably shrink a bit. (By the way, if you were building a workbench in your garage or shed, 'air-dried' timber would be fine, as it would already be stable to the atmospheric condition of said shed or garage.) Finally, if the timber is fresh-cut and green, rough it out well oversize, and allow it to dry in a cool, sheltered airy place for about a year per inch of thickness, then take it inside to condition it to household dryness for a few weeks. That will apply to any 'real' wood - the man-made boards such as ply and MDF are much more stable.
Last thought - oak is a bit too open-grained to make a safe chopping board (stuff can get lodged in the open grain structure). The 'traditional' woods are the close-grained ones like sycamore and beech - these woods are the preferred ones for butchers' blocks, dairy shelves and the like.
