Sure! Here are some YA books (not all are strict romances) about gay/lesbian/bisexual characters with happy endings:
Gay boys:
- Out of the Pocket by Bill Konigsberg
- Boy Meets Boy by David Levithan
- Chulito by Charles Rice-Gonzalez
Lesbian/bisexual girls:
- Starting From Here by Lisa Jenn Bigelow
- Ask the Passengers by A.S. King
- Ash by Malinda Lo
- Adaptation and Inheritance by Malinda Lo (two-book series)
- Keeping You a Secret by Julie Anne Peters
Gender unspecified:
- Brooklyn, Burning by Steve Brezenoff
- Between You and Me by Marisa Calin
Thanks to Queer YA for several suggestions!