Jason Segel is ''totally smitten'' with Michelle Williams while she ''hasn't been this happy in forever''.
The couple have only been dating for three months but pals of the 'How I Met Your Mother' actor say he has never felt this way before.
A source told People magazine: ''Jason is totally smitten. It's like the first girl he's ever been this way with.''
The insider added that Michelle - who has a six-year-old daughter Matilda from her relationship with the late Heath Ledger - ''hasn't been this happy in forever''.
Recently, the pair enjoyed a ''lovey-dovey'' date as they spent a romantic evening watching James Corden's 'One Man, Two Guvnors' Broadway show at the Music Box Theatre on West 45th Street, New York.
An audience member said: ''They look very lovey-dovey. She looks so pretty in white, and he's in a suit.''
Previously, the blonde beauty was seen leaning in and kissing Jason on The Cheek and rubbing his back at the after-party of the premiere of his latest movie 'The Five Year Engagement' in April.
The 32-year-old actor was also spotted holding the 31-year-old star's hand and whispering in her ear at the New York event.
Michelle and Jason have been friends for years after meeting through her friend and his 'Freaks and Geeks' co-star Busy Philipps.