1/2
When Spike reached adulthood, he still started dating Rer. Well, you could say she let him date her out of pity.

The dragon was really glad that they were together and had already planned a lot of things, feeling the most tender feelings for the mare. But it didn't work out to live a lie. Rarity cheated on Spike in a relationship, starting another one, but this time for love.

Everything was revealed when the filly couldn't stand it and told Spike everything as it is. Probably it is not necessary to say that this moment literally broke the dragon and he...He just left Ponyville. He left a note for Twilight saying that he obviously won't be back anytime soon. He needed to find himself, and not try to give himself completely to someone.
After that, Twilight and Rer's relationship deteriorated greatly and they didn't really talk for a couple of years.