Quoting Mrs. Potato Dick:" I always hope that you'll respond to my crisis threads like this one. Heh. It's smurffy to say, and ... [snip!] ... And it makes me sad because I used to look forward to going on Mommy/Son dates to Taco Bell and stuff when he was 2 or 3.."
I know love =( I'm sorry, and this may not sound good, but maybe desensitization will help. . . As in spending time with him doing some fun things will help you reconnect, help you find that good place with him again.
If you are having a really hard time with him, then part of the behavior may be partly due to that. As in, if someone knows they'll get attention for acting bad, they'll do it! So perhaps by fostering some good attention and time for oyu guys, his behavior will get better too. He'll find he doesn't need to act like that anymore.
I think the meds may help too, but I can from personal experience is sucks to go through this on the other hand too. My Mom had a great relationship with my sister, but not with me. We were just so different. I wish she'd tried harder to form a good relationship with me too. It's not easy, because as they grow up they become their own people, and sometimes those people are ones we'd want to kick in the face if they weren't family, lol.
That's the thing though, it might be a vicious cycle. You don't want to be around him because of his behavior, but his behavior DEMANDS a response, so he keeps doing it, making you want to be around him less and making him act up more in response. Maybe some time with just you guys again will help break that.
Maybe someone can watch your daughter and you and your husband and him can spend some time together? He might also feel a little replaced (not your fault, I think all older kids do sometimes) since having your daughter.