No. Now, if it's a constant thing (where he likes every single picture this girl posts), then I'd be suspicious. It's completely natural for guys to like pictures of people they are friends with or who they find attractive. Even when I'm dating someone, I'll still occasionally like pictures that my male friends post.
No. Your significant other is always going to find other people attractive, and you should as well. There's nothing wrong with appreciating the way another person looks. As long as he and you are faithful in all other aspects, there's no harm done.