The court has to decide whether the offence falls into Category 1, Category 2 or Category 3, based upon considerations of both 'harm' and 'culpability'. Once the correct category has been established, a 'starting point' and 'range' for sentencing is then laid down for that offence. See page 178 here:
https://www.sentencingcouncil.org.uk/wp-content/uploads/MCSG-April-2017-FINAL-2.pdf
Given that the offence was 'domestic' in nature, it's unlikely that the offence will be viewed as 'Category 3', so it will therefore be in at least 'Category 2', for which the 'starting point' sentence (from which the court can work up or down) is 6 months imprisonment.
Further, given that a 2-year suspended sentence will have come from a Crown court, rather than from a magistrates' court, sentencing for the ABH offence would normally be passed up to the Crown court, in order that the court can also decide whether to activate the suspended sentence. If the offence which resulted in the suspended sentence being passed was for violence, then there's quite a high chance that at least some part of that sentence being activated.
We haven't got all of the details available to us that the court will know about but, based upon around half a century of reading court reports (and having done a bit of court reporting myself), I'd guess that 'on a good day' your b/f might get sentenced to 6 months imprisonment for the ABH offence (reduced to 4 months if he pleads guilty at the earliest opportunity) without the suspended sentence being activated. 'On a bad day' he could see the 2-year sentence being activated (but with the sentence for the ABH offence running concurrently to it).
So, given that the actual time spent 'banged up' is half of the nominal sentence, I reckon that your b/f could be 'out of circulation' for anywhere between 2 and 12 months.