Vinit Kotadiya told the 13-year-old girl that he loved her and asked her to say the same back to him when he targeted her over a six week period last year.
The 23-year-old also gave the teenager birthday gifts including vodka and £120 in cash in his bid to win her affections while he worked at a store in Tranent, East Lothian.
Kotadiya appeared at Edinburgh Sheriff Court and pleaded guilty to sending the girl electronic messages that were grossly offensive or of an indecent nature and to giving her alcohol between January 1 and February 18 last year.
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Fiscal depute Morgan Beattie told the court the girl was just 13 when she first met Kotadiya outside the Lifestyle Express store in Bridge street, Tranent, last year
Ms Beattie said the shop worker, who now lives in Piershill, Edinburgh, struck up a friendship with the youngster and passed on his Instagram account details to her.
Ms Beattie said: “The complainer followed the accused on Instagram. The accused was informed by the complainer of her age.
“The accused began to buy alcohol for the complainer and arranged to meet the complainer at the back of the Lifestyle Express to hand over the alcohol.”
The court heard the store worker then asked the girl to “be his Valentine’s” in early February last year.
The prosecutor added: “She told him she was only 13 and he said he would wait for her. The accused told the complainer he loved her and wants to marry her.
“He promised not to let her down and again she indicated she was 13.”
Kotadiya then gifted the schoolgirl a new rucksack, a bottle of vodka and £120 in cash when it was her 14th birthday.
The court was told the girl’s mother then “became concerned” about her daughter after spotting messages relating to the gifts between the girl and her friends.
The police were contacted and Kotadiya was arrested and charged.
Sheriff John Cook deferred sentence and will consider placing Kotadiya on the Sex Offenderss Register next month.