I haven't played for long but this is how you get started:
- visit her on the mountain over and over
- Talking to her is important!
- Get milked :D
- repeat
- Do this often enough and you'll get a special cutscene with her in that you can't stop her from being milked.
- You'll then wake up in her home and she'll realize that you got addicted to her venom.
(If you haven't talked to her she'll heal your addiction and nothing will happen but when you talked to her she'll let you ask some questions)
- and after you asked ALL the questions she will ask you if you have feelings for her
- You'll get multiple options on accepting or rejecting her though the choice will probably be obvious ;)
- Don't be surprised if she turns you down. She will tell you if you get addicted a second time she'll consider your love
... That is as far as I got.
Have fun