Matthew Higgins, 30, previously pleaded guilty to three charges relating to sexual activity with a 15-year-old girl last year.
Shrewsbury Crown Court heard that he was arrested last July following concerns that the girl was being groomed by him.
Higgins, unemployed, also pleaded guilty to three offences of harassment relating to phone messages sent to the victim and her family following his arrest.
Sentencing him Judge Peter Barrie said: "It really matters that she was only 15. It really matters that she had her own problems with anxiety and mental health which made her vulnerable and found it difficult to say no to you.
"She has explained in her victim impact statement that after the relationship came to an end she has found that it caused her significant psychological problems on top of the with the problems that she already has," the judge added.
Higgins, of Parklands, in Wellington, blamed his behaviour on the impact of the childhood death of his brother and his father eight years ago.
Mitigating barrister Miss Lynette McClements said the defendant had displayed an "astonishing naivety" in his behaviour towards the teenager.
She also said he had experienced a "shattered and disjointed" childhood and that he was now being advised to get counselling for his issues.
For all the offences Higgins, was given a three-year community order including 30 rehabilitation activity days.
He must attend the Horizons sex offenders' programme and will be subject to an eight-week tag curfew between 7pm and 7am.
He will also be subject to both the sex offenders' register and a sexual harm prevention order for five years.