Deuterium itself isn't an acid, but rather a "heavier hydrogen". It's essentially a hydrogen atom with an extra neutron.
From my knowledge, I know that C-H bonds are slightly weaker than C-Deuterium bonds, consequentially making the H's easier to pull off with a base. I'm not sure if this applies to other atoms than carbon, but the trend probably follows the same one as carbon. This could be the reason as to why having deuterium, instead of a hydrogen, can cause an acid to be slightly weaker, because D is harder to pull off than H.
And as for the SP hybridization -- the reason that hydrogens that are attached to an SP hybridized carbon are acidic is because of the stability of the conjugate base. After the proton is pulled off, the negative charge on the SP hybridized carbon is stabilized because of the greater S character that an SP orbital has. Greater S character equates to more stability in housing a negative charge because of the more spherical shape vs. the more dumbbell shaped orbital that you would get from having more P-character.
Basically, more S-character in an orbital allows the negative charge to get closer to the positively charged nucleus, which is a good thing (negative likes to be close to positive). However, with the addition of more P-character (such as an SP3 hybridized carbon), the negative charge has "more room" to move around per se, because the dumbbell shape that the P-orbital accompanies allows for this movement away from the nucleus.
If you need me to clear anything up, let me know! I feel as if my explanation may be a bit vague 😛
