Jenelle Evans and Gary Head in Fayetteville, North Carolina, January 17, 2012. Credit:

Jenelle Evans is officially off the market!

The Teen Mom 2 star is engaged to her on-again, off-again boyfriend Gary Head, a source confirms to Us Weekly. first broke the engagement news and Evans, 20, tweeted a photo of her engagement ring Wednesday, writing, "I'm the luckiest girl in the world to have Gary Head in my life."

"Gary asked her to marry him last month," the source tells Us. "She wasn't certain about Gary and didn't want things to be that serious between them."

Evans and Head's relationship has been on and off for over 5 months. On April 8, Evans tweeted, "I'm very depressed. Me and Gary broke up for good." And she briefly reunited with her former flame, Kieffer Delp, at the end of April before calling it quits again.

Head, 22, supported Evans through her boob job earlier this month, in which the single mom went from a B to a "full C."

"Gary took care of her when she was recovering, and that made it solid to her, that he was really there for her," the source adds. 

As for Evans' brand-new bling?

Evans proudly flaunts her new engagement ring in her Twitter photo.

"The ring is a princess cut solitaire diamond," the source says, adding that Evans is head over heels for her man.

"She's in love with him entirely."