My dad thinks I'm going to end up with guy

On the one hand: yes, you have every right to be annoyed by this. It can be infuriating when people profess to be accepting, and then occasionally let slip that they have no clue about how ignorant they are.

On the other hand: you said it yourself: it took you a lot of time to be able to accept this. And... the moment you came out was one of the final parts of accepting.
To him, however, this was the beginning. He didn't feel your internal struggle. For him, this was something that suddenly came out of left field.
It's only natural that it takes him a good while to understand and accept as well.

So: don't get too upset. He may not understand fully, but he probably is trying. In the meantime, the best you can do is to remain calm, and keep acting casual about your sexuality. If he mentiones "turning straight" as an option, casually dismiss it as "It doesn't work that way and I'm quite happy the way I am". Don't get baited into discussions and just state this as a fact.
It'll take weeks, even months, but it'll sink in eventually!

 

Don't be so tough on him. In a lot of cases, parents are just trying to look out for you in their own misguided way.

In your case it's likely your dad just wishes for you to be happy, but happiness for him is family so that is what he hopes for you. It's hard to deal with issues like this when your ability to relate is literally 0%. He probably didn't even know he was being hurtful.

Keep in mind that I don't know your family though, I'm just taking shots in the dark to try and give you ideas that might apply.

 

I've been in a similar situation with my mom. When I first came out to her she seemed to be pretty accepting and understanding and we didn't talk about it for a while after that. Then the second time it was brought up she said something along the lines of "well you aren't a lesbian right?" she thought I liked both which was completely fine to her. She wanted me to end up with a man and have a child so that she could be a grandmother. She started telling me not to post stuff on Facebook that were LGBT related, because she didn't want others to know especially my relatives. She came to me and told me this quite a few time. She also told me things like "I still have hope that you might end up with a man" it frustrated me to no end.

My brother is also gay and right off the bat she was accepting, I even came out to her first and it took her longer to be okay with my sexuality. I guess eventually she saw that my sexuality wasn't going to change, I'm not sure how she ended up dealing with it, but she did and that's the important part. Now she tells me she wants me to find a girlfriend, funnily enough.. she has even tried to introduce me to a girl.

So I know somewhat how your feeling and I think anyone would be upset by this so I don't blame you. Nobody knows for sure and I don't know how long your dad has known about you, but don't lose hope that maybe one day he will be accepting or at least more accepting. It is hard to see how difficult it might be for parents, because your the one who had to go through all that not them, but just try to be patient and keep your cool in situations like this one.