He is being lied to by his girlfriend who is telling him that she has liked him for five years.
"He is being lied to by his girlfriend"＝「彼は彼女に嘘をつかれている」
"who is telling him that "＝「その彼女は彼に～と言っている」
"she has liked him for five years"＝「彼女は彼を5年間好きだったと」
Sentence in context:
"I'm afraid that his girlfriend has been lying to him by saying that she has liked him for five years. It's unfortunately not true."
She kept telling him she liked him for over 5 years, but it was all a big lie.
She has been confessing her love for him for the last five years, but it turns out she's a big fake.
「彼が嘘をつかれていた」わけですが「彼女が嘘をついていた」と言うことの方が多い気がします。
ーShe kept telling him she liked him for over 5 years, but it was all a big lie.
「彼女は彼を好きだと5年以上言い続けてたけど、それは全部大嘘だった。」
keep telling him ... で「彼に…と言い続ける」
for over 5 years「５年以上・５年にわたって」
a big lie「大きな嘘」
ーShe has been confessing her love for him for the last five years, but it turns out she's a big fake.
「彼女はこの5年間彼への愛を言い表していたが、彼女がとんでもないペテン師だとわかった。」
confess one's love で「愛を言い表す・打ち明ける」
for the last five years で「この5年間」
turn out 「…だとわかる」
a big fake「とんでもないペテン師・詐欺師」
ご参考まで！
She'd been lying about her five years of love for him.
She had been lying to him that she liked him for five years.
こんにちは。
様々な言い方ができると思いますが、例えば下記のような表現はいかがでしょうか：
・She'd been lying about her five years of love for him.
彼女の彼に対する5年間の愛は嘘でした。
・She had been lying to him that she liked him for five years.
彼女は、5年間彼のことが好きだったと嘘をついていました。
今回は she を主語にした英文がすぐに思いつきました。
ぜひ参考にしてください。
アメリカ合衆国 
カナダ 
