They have a deep sexual attraction to one another.
Advanced English Dictionary
+adjective 1[usually before noun] connected with the physical activity of sex: sexual activity / behaviour / desire + They were not having a sexual relationship at the time. + Her interest in him is purely sexual. + sexual orientation (= whether you are heterosexual or homosexual) + a sexual partner (= a person who you have sex with) 2[only before noun] connected with the process of producing young: the sexual organs (= the penis, vagina, etc.) + sexual reproduction 3[usually before noun] connected with the state of being male or female: sexual characteristics / differences sexually adverb: sexually abused children + She finds him sexually attractive. + sexually explicit + Girls become sexually mature earlier than boys. + The disease is a threat to anyone who is sexually active.
Random quote: You will not be punished for your anger, you will be punished by your anger.: Buddha