Formal:
* Gusto ko lang makasama ka. (This is the most literal translation and is appropriate in formal settings.)
* Nais ko lang na makasama ka. (This is another formal option, using a more literary word for "want".)
Informal:
* Gusto lang kitang makasama. (This is a more casual way to say it, using the familiar form "kita" for "you".)
* Ang gusto ko lang, makasama ka. (This emphasizes your desire to be with the person.)
* Sana makasama kita. (This translates to "I hope to be with you," and expresses a wish.)
Romantic:
* Ikaw lang ang gusto kong makasama. (This means "You're the only one I want to be with.")
* Nais kong makasama ka sa lahat ng oras. (This means "I want to be with you all the time.")
Remember: The best translation will depend on the context of the situation and your relationship with the person.