For me #Define "soulmate" is a person who you can rely on, day and night. But I think this soulmate-ship doesn't need to last until either one dies. Just as with any friendship actually. I think it is unrealistic to think a friendship lasts until either death. Friends come and go, that's just how it is, and it's not bad.
I think, in accordance with what the others said, one should not be going looking for a soulmate. I think you can come across people, who can become friends, and friends can maybe become soulmates.
1. Can a soulmate be someone you hate but supports you at the same time?
2. What if there is some connection between you and the other one (e.g. if you get hurt, the other person would feel it too)?
3. Does a "soulmate" need to be a human (e.g. an animal, ghost/soul such as "Beyond: Two souls")
1. Yes. I've several times hated my friend (who I consider to be very close to me) for being truthfully honest with me. All they did was holding up a mirror in front of me and confronting me with the uncomfortable truth I didn't want to see.
2. As a human being, I feel empathy. Sometimes so much that it hurts me. It's a belly/heart feeling. I think you seek the answer to: "Is there an actual link between souls". Which I think, no one can prove or disprove
3. I don't know. I think some people love certain objects (Their car), or animals. This however does not always allow relying on said object or animal. I think an animal can comfort you when you're sad, but If you have financial problems for example, I don't think they can actually help you to pay the bills or make a plan of action. So I'd like to stick with soulmates as being sentient human beings.