He's not respecting your boundaries, and that is a huge problem. It doesn't matter if he grew up in a "touchy-feely" family. He doesn't have a right to make you uncomfortable because of his physical needs. Why isn't he cuddling with his wife, your mum? I suggest discuss the issue with him openly, during the daytime. Perhaps your therapist can host him in the office and mediate for you. Let him know that you feel uncomfortable and don't want to share a bed with your parent at this age. Lock your door if you can, or put a chair in so it can't be opened. If he persists, report this to some other trusted adult. The fact you feel uncomfortable is reason enough.
Wow, hard situation. What's up with your dad, right? Yeesh. Have you tried to have the conversation publically in front of your mom like during dinner. "hey dad, I'm older now and having you sleep with me causes me not to get a good nights rest which I need. So, I'd like to ask you to let me sleep alone from now on so I can get my full rest." (I guess I was putting it off on your not being able to sleep soundly because then he may not get as defensive or argue as much). Then your mom can chime in "yes, that sounds right. You need your rest so sleep alone from now on. You can agree to that, right X (your dad's name)?" Or you are older now, get up and go sleep on the couch if he comes into your room. If he gets mad, that's his problem. Or have an air mattress handy or just a sleeping bag and roll it out and sleep on the living room floor. If he gets mad -- so what. Again, his problem. You can say that you told him that you do not want to sleep with anyone. And you meant it.
Agree that it is your right to sleep alone. So, make it happen. I'm surprised your mom is not more supportive to you. She needs to tell her husband too to back off. Is he a hot head where she is afraid to upset him? Anyway, try the direct approach during day light hours in front of your mom and if he comes into your room to lay with you, get up and go to the couch or sleeping bag as a statement that you meant it. good luck and let us know how it goes
If it makes you uncomfortable, he should not be there. I am not implying there is anything sexual going on either (it's more likely he is just nostalgic that you are growing up and soon to be out) but if you don't want him in your bed you have the right to insist. Any child deserves his privacy, 7 or 17. I would tell him this and then either get up and leave if he is there, or just put a lock on the door and lock it at night. (A simple hasp lock from the hardware store would do.) I'm sorry it would have to come to something that obvious, but your dad is not getting your hints or believing your direct statements, and he needs to get a clue. He has no right to get mad at you for wanting him out of your own bed. Anyway, my guess is this has nothing to do with your sexuality at all except as it represents you growing up, and is more about fear of, or sadness about, change. But even so, high school is a touchy enough time without a dad doing something kind of unwanted.