It's really a nightmare of Inter who were leading the table from the very first and with a few matches (4) left, they have slipped to the 2nd place. Their win on champions league too might have cost the position in the league as they are overworked. It's not hard to predict that they'll lose on both front. Napoli has rest of its three matches with easier teams and they would do all they can to secure 3 points on them. On the other hand, Inter needs to play with Lazio and even if they won all their 4, they would still be 2nd unless Napoli loses and draws some. Which is very unlikely. Similar is with Champions league where Barcelona may overpower Inter.
Of course, how can i blame you? As usual, Inter is Inter as usual, after all.
They play well all season and then at the end of the season they play badly and are overtaken. Among other things, Napoli have easier matches, while Inter will have to challenge tougher teams.