"He feels so blessed to have her in his life and to call his person. He is obsessed with her and loves being with and talking to her every day, even if it's about silly little things over text message."
The source added, "They have a lot of fun together. Colton has also gotten very close with Cassie's sister, Michelle, and Michelle's boyfriend, Gregg Sulkin, as well as a bunch of Cassie's best friends."
While Colton, 29, has reportedly been ready to pop the question, Cassie, 24, has needed more time.
"Colton has talked about proposing to Cassie sometime in the next few months, but he knows that she is not in a rush to get married," the source explained.
"She was pretty hesitant about their relationship at first, but she ultimately fell for Colton and now loves him."
Colton starred on The Bachelor's 23rd season and fell in love with Cassie on the show.
Cassie obliged and then traveled to Spain to meet Colton's family while cameras were still rolling. Once the show ended, Cassie slowly fell in love with Colton in the real world.
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Although Cassie loves Colton now, his feelings are reportedly still further along than hers.
"At the moment, he definitely has stronger feelings than she does, though," the source told Us.
"Cassie grew up with very traditional values. The thought of taking the next step in their relationship scares her at times because she is still very young."
After going public with their romance in March following The Bachelor finale on ABC, Cassie and Colton spent a lot of time traveling for events and public appearances.
The couple's romance has definitely been a slow burn. Colton, for example, relocated to the Los Angeles area after the show to be closer to Cassie, but they didn't even move in with each other.
Colton told Extra back in April he could envision himself proposing to Cassie "within the next year," and then a month later, Cassie told Us, "We really don't have a timeline... We're just enjoying right now and not worrying about it."
Colton added at the time, "[We] don't want to rush something that's going to last forever... We want to build such a strong foundation for ourselves to use to sort of launch us for the rest of our lives, and that's what we're doing."