|I think he kept the ring because it was the one that Keith used to propose to his mom, not because he used it to propose to Peyton.|
I really really believe Peyton lied to Lindsey about the ring. Prior to that scene, there hasnt been even ONE mention or clue that tells us that ring belongs to Karen but we have been given every reason to believe its not:
1. Lucas going to LA in 505 was a spur of the moment kind of thing, so unless he had the ring with him in the basketball game, it couldnt have been Karen's, he was on the bus and he told Whitey to drive him to the airport.
2. His proposal speech said that that winning championship was great but he realized that it didnt mean anything unless she was there with him further indicating that he made the decision to propose to her AFTER winning the game.
3. Brooke saw Karen's ring close up in S3 on Karen's hand (bought it right up to her face, freaked out about it etc), but when she saw it in 505, she acted as though she never saw it before, even saying that she wants to look at it to study it and give her honest opinion on the ring---why would she do this unless it was new?
4. Brooke asked if he even bought a ring for the proposal and he showed her the ring, which in simplest terms meant he DID buy a ring.
5. If it WAS Karen's, why didnt Lucas tell Lindsey it was? When guys propose with their mom's/grandmother's/etc's ring, they SAY it to show how important it is and the history it carries. So why did Lucas leave this out?
Following what was said in that sentence, we know Peyton lied about the proposal, he DID propose to her but she said he didnt to pacify Lindsey, so its logical (imo) to think she would lie about the ring too to make Lindsey "stop doubting it".
If I was Peyton, I still don't know how I'd feel about it all. He was still willing to do forever with someone else, no matter how convinced she is he loves her. That would still weigh on my mind.
Divorcees sometimes remarry, so its not impossible to think that some people wouldnt not feel right about being with someone who wanted to spend the rest of their lives with someone else once. Plus as I pointed out in the LP thread, Keith almost married Jules but we fully believe that he loved Karen, and she didnt doubt it herself when she returned his love. Dan married Deb but in S4 when DK were getting close, she didnt hold it against him and its very evident that Karen is the only women Dan ever really loved selflessly. Outside of OTH, Ross married countless times but he knew that when he got together with Rachel she was going to be it, she didnt doubt his love and devotion and neither did the audience.
And of course, the most important fact to consider here is that Peyton has NO right holding this against Lucas, why? Because she proposed and was going to marry Jake in S3 and it would have happened if Jake didnt back out, just like Lucas' marriage would have happened if Lindsey didnt back out. Both times, it was because they knew Lucas' and Peyton's heart belonged to someone else.