Sebastian had set plans for the future before he ended up with you. Leave Stardew Valley, move to the city and make a new life for himself. So, it'd be safe to say that his past self would be insanely shocked at how he turned out. Still in Stardew Valley but freed of his basement, and married, with a child, and due a second one.

Falling in love and moving in with you was like the biggest reality check for him. He learnt that the valley wasn't the problem, but how he was living, the city would never have helped him and what he needed was a truly stable relationship. He often helped around the farm and was honestly, a great father, picking them up and walking home with them after they spent the day in town with Jas and Vincent.

One day, it was still pretty early in the morning, and somehow, Sebastian ended up awake before you, so, since he had been learning to cook, he finally took it upon himself to use his new skills and cook breakfast for when you woke up since he knew, that soon, you'd most likely be up too.