I had a dream about finding a half seal half lamb in my kitchen with most of its legs cut off and I felt terrible but felt I had to cut off it’s stubs and then drop him in the sink and kill him all the way and while I was doing this he was just looking at me and I felt absolutely terrible the whole time.
What do you think this could mean? 
Well, I’ll say that you have recently had a fight with a partailly mentally-ill person (Or mentally defected) that you don’t seem to like too much (That is, you want to be their friend, but you would not be their best friend or anything alike), but likes you very much (as a friend) and depends on your support (as a friend, although they don’t talk with you about life).
You may have not actually fought with them, but rather simply stopped talking with them. (Much more probable than the first option)
“They” are probably male.
You realy don’t like to be seen hanging around with them somewhy. Meaning they haven’t many friends.
Sounds just like something I would have dreamt…
That can’t be right I don’t know anyone with a disability like that, or have had a fight with anyone recently.
if it was my dream…
lamb implies innocence to me
seal … sealed lips … also seal culling comes to mind.
so the idea of something vulnerable
legs cut off … could be not being allowed to do some things, having your options limited
and then with the trimming … obeying the limits set by others.
the killing could be that reducing the available paths reduces full choice and so kills some ambitions/hopes
or taken literally, it could be questioning moral choices of how we live … is it right to butcher the natural world for our own gains?
If you put it that way, it sounds like my life. 
I am not a very big believer in symbolism to an extent. For instance, I had a dream last night where me and a bunch of other kid’s school crashed down onto a beach. I certainly hope that isn’t symbolising much…but we all have to dream about negative emotions sometime. I would compare the emotion you felt in your dream to the same emotion you felt recently in real life (I dreamt that I got really mad at my sister once, and I do sometimes feel that way IRL.) But it could, and probably is, just random.
Could it be, that IRL you feel that you should “kill” something that is very dear to you, and you feel sad of doing it, but you know that you need to. This “dear thing” might be some habit, some relationship, or smt. like that.
?