I have a teenage DSS and have been around since he was young. He lives with us, we also have 2 younger DCs.
I love DSS, no question about that, however, for me, it isn't that Unconditional Love I have for my own. He's a good kid and I get along very well with him, I go out of my way for him, but he isn't mine.
DP knows how I feel, and says he loves me more due to the fact that I put myself out for him, that I do all his washing, ironing, cooking, give him lifts, etc.
I explained to DP that I love him much like I love my siblings or even DP, I'd do anything for them, but sometimes, things they do, can annoy me, like chewing loudly for example. I'd never voice this annoyance, I'd simply put my feelings away to not upset them, which is compromising when it comes to love. However, the unconditional love I have for my DCs, I can't ever imagine feeling annoyance at trivial things.
So my point is, if your DH is kind and fair to your DC, I think he's doing a great job.