I don’t understand my dad

I’M 20 years old. Once, I was a bubbly, happy-go-lucky girl. However, things changed when my father retired three years ago. He has become a changed man. Instead of respect, I now feel constantly annoyed with him.
When he first retired, I could still endure the changes as I thought that it was a transitional period before he got used to retired life. However, he has become increasingly annoying. Perhaps, he still thinks that I’m seven.
I notice that these days he prefers to speak to me at a very close distance (when he can actually choose to speak louder). This terrifies me, seeing him standing right up close in front of me. He follows me everywhere I go in the house. The list goes on. When I feel uncomfortable with his acts, and explain it to him, he just laughs.
I’ve even made use of the whiteboard in my house to explain to him how I feel, but he just ignores the messages. Sometimes, he even alters the messages to something really different (for example, hate becomes like, annoying is changed to lovely).
I am currently waiting for a place in a public university. It worries me that I still need to stay at home for so long before I can move out to further my studies in July. Besides, I’m also worried about my mom’s safety because my father still has some sexual urges. My mom has already given up hope on him even though she hasn’t filed for a divorce. It’s not convenient for me to elaborate on my situation further as I too feel embarrassed about this.
I just hope to end this nightmare as soon as possible for I’m worried if this goes on, I will need to see a psychiatrist. Is there any effective solution for me to tell him to stop doing such things?
Please Help

Perhaps you need to understand your father before you put him away as an annoying, weird old man who has been acting strangely. If his behaviour has undergone some drastic changes, then perhaps he needs medical help, not you.
Some retirees find it difficult to adjust to a life without purpose. They do not know what to do with their time after working hard for years without a break. Your father could feel this way and have been trying to get some attention from you. Perhaps he feels guilty for not giving you enough of his time and love when he was working.
You should also check if he’s got a hearing problem. Standing close to you could be the means to hear you better. If he is annoying, irritating and seemingly oblivious to your true feelings about him, it could be his way of blocking out the truth. Perhaps he simply does not want to know that no one cares about him or needs him at home.
You write that your mother has problems with your father. But in what way does his sexual needs spell danger for your mother’s safety? And why are you embarrassed that your father still has a need for sex? Your feelings for your father seem strained. Could it be that you feel sexually threatened as well?
Understand your fears. Talk to your mother. Do not see your father as someone your mother cannot love and whom you seem afraid and irritated with. Perhaps he needs help. Leaving home is an easy solution but will you be able to cope with your feelings towards your father?
You must not try to run away from the feelings that are bothering you. If you need to consult a psychiatrist, do so. You have to understand so that you do not have to suffer such fears about your own father.