Given the following context:

"Missing My Baby" is a mid-tempo R&B ballad with influences of urban and soul music. It is in the key of D major, at 144 beats per minute in common time. The recording incorporates melisma, with sung poetry during the downtempo part of the song. The melody is accompanied by backing vocals, and instrumentation is provided by an electric piano, drums, a keyboard, a synthesizer and strings. Contemporary music critics praised Selena's emotive enunciation, which emphasized the song's title and central theme. R&B duo Full Force were the backing vocalists for the original and remix versions of "Missing My Baby".J.R. Reynolds, formerly of Billboard, called "Missing My Baby" a "dreamy ballad" with an "R&B-styled melody under Selena's pop vocals". Ramiro Burr of the Austin American-Statesman described it as a soul ballad. Jerry Johnston of the Deseret News thought that Selena displayed a "Leslie Gore [sic] baby-voice" in "Missing My Baby" and that she "displays a wonderful suppleness in her voice". The Virginian-Pilot said that the song was built on hooks that recall Diana Ross's "Missing You", which is a tribute to Marvin Gaye, and the Beach Boys' "Good to My Baby".The song begins with a drum solo before the other instruments enter to form the musical foundation. Selena sings to her absent lover about how much she misses him, saying that he is "always on [her] mind" and that she feels lonely when he is not with her. Three times she sings, "I often think of the happy times we spent together / And I just can't wait to tell you that I love you". In the chorus, she sings of wanting to hold him tight and feel his heartbeat.

answer the following question:

About whom is Selena singing of wanting to hold him tight and feel his heartbeat? 

her absent lover