Your H sounds like the horrible person, forcing you to have a pregnancy you didn't want, laughing at your deepest feelings, and then despising you for your very natural unhappiness. Having children is very hard work in all departments, not least emotionally, and he's just dumped this on you and has the nerve to laugh at your pain, and then tell you you are wicked for being sad. Insensitive arse!
Don't feel guilty about DS3. We can't help who we love. Although of course it isn't his fault that he is mixed up with all this negativity, it isn't yours either. (I would trot out "he didn't ask to be born", but then neither did you or I.) How can you relax enough to feel warm and loving, when the child's very existence says "your feelings do not matter"? At the same time, I hope you manage to treat him with as much kindness and consideration as you would any of the others, and realise that he is as much a victim as you are of his dad's insistence he should be brought into the world. One day you may well fall in love with him. It's very likely your H's onging refusal to acknowledge your bitterness which is getting in the way of this.
Not that it's anything like the same, as I did mean to have him, but I had trouble bonding with DS4 as I seemed to be "all loved out" and, as the other three got older, no longer able to engage with babies. (In hindsight probably the onset of depression.) With my eyes I saw a lovely child, as indeed he was, but with my heart I didn't see one that was really mine, somehow - just a little stranger I had to cope with. I used to hold him close every day and murmur "I love you, baby", and one day I realised it was true. Today he's a lovely young teen of whom I am so proud, and still loves his cuddles! His dad, on the other hand, is not on the scene...