Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
lovesick [ˈlʌvsɪk] adj томи́мый любо́вью
to be lovesick томи́ться*(impf) от любви́
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
Русский: