Reese Witherspoon and Jim Toth are heating up.
They were among the guests at Colin Hanks' wedding to Samantha Bryant at the London Hotel's rooftop in West Hollywood Saturday.
Sitting next to Alyssa Milano and her husband and a few rows behind Tom Hanks and wife Rita Wilson, "they seemed totally in love and were holding hands for most of the ceremony," a source tells UsMagazine.com. "Jim had his arm around Reese's back, and she rested her head on his shoulder. Reese was listening to every word that was said and she would laugh at the funny parts and then turn to Jim."
At the end of the ceremony, "Jim pulled her in close and kissed her on the lips and cheek and then gave her a long hug," adds the onlooker. "Watching other people say their vows really brought out the love in them. They were very sweet and affectionate."
As they exited, "they held hands and said 'hi' to people," the source tells Us. "Then they walked over to the pool area for cocktails."
Earlier that day, they cheered on her son Deacon, 6, as he played soccer in L.A.
The two have been dating since February shortly after her split from Jake Gyllenhaal.
A source recently told Us that Witherspoon, 34, and Toth, a 39-year-old agent at L.A.'s Creative Artists Agency, "started as friends, and it developed into more."
Not only has he been spending quality time with her kids (they all went to a church service on Easter), he also helped her celebrate her 34th birthday with a romantic weekend getaway in Ojai, Calif.
Says a source, "It's hot and heavy."