At this age this sort of thing can be as much about power games as about genuine comfort.
Of course it is upsetting for your dh, but he must be chilled about it. Eventually the LO will come around to him. Don't put any pressure on the LO to go to Daddy.
A couple of things that can help:
Do you always find yourselves splitting up with dh taking dc1 and you taking dc2? If so, try to break that pattern fro time to time, even if it's just who holds whose hand when walking down the street, and even if it's only for a few minutes. But you can also take the other child out, to the shops or to a playgroudn etc.
When dc2 falls over, or needs comfort, don't rush to him - let dh go to him. If dc2 says "Not Daddy - want Mummy", then daddy says, "OK, let's take X to Mummy" and does so. No fuss.
If he won't give dh cuddles, dh could try asking him to catch Daddy's kisses. You might have to model it for him, blowing kisses to each other and 'catching' them dramatically.
The important thing is not to put any pressure on him, not show him that you are upset by this, but to offer him as much as he is able to accept and show him that you (both of you) are ready for him to become more affectionate with his daddy.