You are not unwanted. You can't choose how your family reacts. You should not let things get to you. Have you tried seeing if you can get help moving to a different place or seeing if they will provide a place for you to live so you don't have to live there. No family is perfect. Try not to even start harming because once you do it will be extremely hard to stop once you start. You need to remain strong and be the better person. Have you thought about getting counseling or seeing a psychiatrist? You need to get some help.

I am sorry that you are feeling this way. Maybe talking with your mom about how you feel when she takes his side all the time. Parents cant read minds, and sadly sometimes during stress and when two people start to have issues between relationships they try and block things out which might feel like she is taking his side. Talk thats the best way to really know..
Wanting to be adopted may not give you the love your looking for... most parents that are looking are looking for children that are young, babies young children not the older teen or preteen. So you would end up in group homes or in foster homes and that is not always what your looking for... sometimes if you think you would be better off living on your own and joining the real world having to work and pay bills and grow up and have added stress of paying pulls and rent you can ask to go on social assistance to help get you started, but again its not all what it is cracked up to be.

I might sound harsh, but it seems they are just not showing you that they love you... and that could be do to the fact they dont know how to show it, or they are so blocked out that they dont know how they are making you feel. either way its not right, everyone needs to feel loved and wanted.

Talk to them, it might sound stupid but if they ready didnt want you then they would both tell you, And to the worse they would kick you out if it was true...

Being a teen is very tough and even more so when you dont feel wanted more so by your own parents.

stay strong you will get through this, most teens that have protective parents wish to have parents like yours so they can be alone in their room.
I had parents that didnt care, and step parents that didnt care and I always wished I had parents that did, but seeing some of my friends and their teen daughters I would have flipped if my parents did that to me when I was a teen.
You cant choose the parents you get and no matter which type of parents you have at some point you wish they where different.
Hang in there, there is no need to cut over their loss. One day you will be out on your own and they will have missed out, and you wont want them in your life.
Take care, stay strong.