I understand wanting to keep his stuff around as a token reminder of him (I have a house, closet, drawers and garage) full of H's things... And I have no desire to remove them.

IMO: Your issue is more with the fact that he's using your sons as a loophole to your boundary agreement, and that's disrespectful. I'm with nhmom, let this one slide, but of it happens again- you have every right to calmly remind him of your previous agreement and that you don't appreciate him putting your kids in the middle of a situation that is between you and him. (I think part of your irritation is the mama bear coming out to protect your kids from something that shouldn't be their drama to solve.)

M-31, H-31
T-9, M-7
S-6, s-20mth
sep 8/1/11
ILYNILWY 11/29/11
Creating separation papers.
Discover H has feelings for BFF, she does too 1/11/12
H moves out 1.20.12