What if you get isekai'd but the main heroine of your story is not to your liking?

What if you get isekai'd but the main heroine, the first girl (whatever title she may have) of your harem and she's not to your liking. She's into you and she's clingy. How should one respond without hurting her feelings or being disrespectful? Or is the protagonist of the story stuck with her until she dies eventually from old age? (Fingers crossed she's not from one of those magical species who can live for multiple centuries.)